Display device, electronic device, and operation method thereof

ABSTRACT

A method for operating an electronic device with lower power consumption is provided. The electronic device includes a display device and a touch sensor. In the case where the touch sensor senses no touch, the touch sensor is brought into a resting state or operated so as to perform a sensing operation at a reduced drive frequency. Also in the case where the touch sensor constantly senses touches and an image on the display device is not changed, the touch sensor is brought into the resting state or operated so as to perform the sensing operation at a reduced drive frequency.

BACKGROUND OF THE INVENTION 1. Field of the Invention

One embodiment of the present invention relates to a display device, anelectronic device, or an operation method thereof.

Note that one embodiment of the present invention is not limited to theabove technical field. The technical field of the invention disclosed inthis specification and the like relates to an object, a method, or amanufacturing method. Furthermore, one embodiment of the presentinvention relates to a process, a machine, manufacture, or a compositionof matter. Specifically, examples of the technical field of oneembodiment of the present invention disclosed in this specificationinclude a semiconductor device, a display device, a liquid crystaldisplay device, a light-emitting device, a power storage device, animaging device, a memory device, a processor, an electronic device, amethod for driving any of them, a method for manufacturing any of them,a method for testing any of them, and a system including any of them.

2. Description of the Related Art

Display devices included in mobile phones such as smartphones, tabletinformation terminals, notebook personal computers (PC), portable gameconsoles, and the like have undergone various improvements in recentyears. For example, there have been developed display devices withfeatures such as higher resolution, higher color reproducibility (higherNTSC ratio), a smaller driver circuit, and lower power consumption.

For example, an improved display device has a function of automaticallyadjusting the brightness of an image displayed on the display device inaccordance with ambient light. An example of such a display device is adisplay device having a function of displaying an image with reflectedambient light and a function of displaying an image with light emittedfrom a light-emitting element. In this structure, the brightness of animage displayed on the display device can be adjusted in the followingmanner: the display device is set to a display mode for displaying animage with the use of reflected light (hereinafter referred to as afirst mode) when ambient light is sufficiently strong, whereas thedisplay device is set to a display mode for displaying an image with theuse of light emitted from a light-emitting element (hereinafter referredto as a second mode) when ambient light is weak. In other words, thedisplay device can display images in a display mode that is selectedfrom the first mode, the second mode, and a mode using both the firstand second modes (hereinafter referred to as hybrid display or a thirdmode) in accordance with the intensity of ambient light measured with anilluminometer (also referred to as an illuminance sensor in some cases).

As an example of a display device having a function of displaying animage with light emitted from a light-emitting element and a function ofdisplaying an image with reflected ambient light, Patent Documents 1 to3 each disclose a display device in which one pixel includes a pixelcircuit for controlling a liquid crystal element and a pixel circuit forcontrolling a light-emitting element.

In this specification, such a display which includes a light-emittingelement (e.g., an organic EL element, an inorganic EL element, or anitride semiconductor light-emitting diode) and a reflective element (areflective liquid crystal element) as display elements is referred to asan ER-hybrid display (an emissive OLED and reflective LC hybrid displayor an emission/reflection hybrid display). A display which includes atransmissive liquid crystal element and a reflective liquid crystalelement as display elements is referred to as a TR-hybrid display (atransmissive LC and reflective LC hybrid display or atransmission/reflection hybrid display). In addition, a display devicewhich includes a light-emitting element and a reflective element asdisplay elements is referred to as a hybrid display device, and adisplay including the hybrid display device is referred to as a hybriddisplay.

REFERENCE Patent Document

[Patent Document 1] United States Patent Application Publication No.2003/0107688

[Patent Document 2] PCT International Publication No. WO2007/041150

[Patent Document 3] Japanese Published Patent Application No.2008-225381

SUMMARY OF THE INVENTION

When a display device includes a touch sensor portion as an inputinterface, a user can operate an electronic device including the displaydevice by touching a display screen or making a touch gesture. Asexamples of a method for providing the touch sensor portion, there is amethod in which a touch sensor unit is placed over the display screen ofthe display device (out-cell) and a method in which the touch sensorunit is provided inside the display device (on-cell). Furthermore, adisplay device including a liquid crystal element can have a touchsensor function when a common electrode of the liquid crystal element isused as a touch sensor electrode (full-in-cell).

In an active matrix display device including a liquid crystal element,when a transistor whose channel formation region includes a metal oxideis used as a transistor included in a pixel circuit of the displaydevice, the transistor can have an extremely low off-state current. Thatis, image data written to the liquid crystal element can be retained fora long time.

Here, a description is made on a display device with a full-in-celltouch sensor in which the transistor whose channel formation regionincludes a metal oxide is used as a transistor included in a pixelcircuit and a common electrode of the liquid crystal element is alsoused as a touch sensor electrode. In the case of the full-in-cellstructure, an image writing period and a touch sensing period areprovided. A touch sensor portion is preferably in a resting state whileimage data is written to the liquid crystal element. This is because thewriting of the image data causes a noise. During the touch sensingperiod, although the transistor is in the resting state in order thatthe liquid crystal element can retain image data, the touch sensorportion keeps sensing even without the user's touch. Therefore, a largeamount of power might be consumed for the sensing.

An object of one embodiment of the present invention is to provide anovel display device. Another object of one embodiment of the presentinvention is to provide an electronic device including a novel displaydevice. Another object of one embodiment of the present invention is toprovide a method for operating the display device or the electronicdevice.

Another object of one embodiment of the present invention is to providea display device with low power consumption. Another object of oneembodiment of the present invention is to provide a novel driving methodfor touch sensing.

Note that an object of one embodiment of the present invention is notlimited to the above objects. The above objects do not preclude theexistence of other objects. The other objects are the ones that are notdescribed above and will be described below. The objects that are notdescribed above can be derived from the description of thespecification, the drawings, or the like by those skilled in the art.One embodiment of the present invention achieves at least one of theabove objects and the other objects. One embodiment of the presentinvention does not necessarily achieve all the above objects and theother objects.

(1) One embodiment of the present invention is a method for operating anelectronic device including a display device and a touch sensor. Themethod includes a first step, a second step, a third step, and a fourthstep. The first step includes a first judgment step of judging whetherthe touch sensor has sensed a touch in a first period, a step ofproceeding to the second step in the case where the first judgment stepconfirms that no touch has been sensed, and a step of proceeding to thethird step in the case where the first judgment step confirms that atouch has been sensed. The second step includes a step of bringing thetouch sensor into a resting state or operating the touch sensor at areduced drive frequency. The third step includes a second judgment stepof judging whether the display device has been brought into a restingstate or has operated at a reduced drive frequency, and a step ofproceeding to the fourth step in the case where the second judgment stepconfirms that the display device has been brought into the resting stateor has operated at the reduced drive frequency. The fourth step includesa third judgment step of judging whether touches have been constantlysensed, and a step of proceeding to the second step in the case wherethe third judgment step confirms that touches have been constantlysensed.

(2) Another embodiment of the present invention is a method foroperating an electronic device including a display device and a touchsensor. The method includes a first step and a second step. The firststep includes a first judgment step of judging whether the touch sensorhas sensed a touch in a first period, and a step of proceeding to thesecond step in the case where the first judgment step confirms that notouch has been sensed. The second step includes a step of bringing thetouch sensor into a resting state or operating the touch sensor at areduced drive frequency.

(3) Another embodiment of the present invention is a method foroperating an electronic device including a display device and a touchsensor. The method includes a first step, a second step, and a thirdstep. The first step includes a first judgment step of judging whetherthe display device has been brought into a resting state or has operatedat a reduced drive frequency, and a step of proceeding to the secondstep in the case where the first judgment step confirms that the displaydevice has been brought into the resting state or has operated at thereduced drive frequency. The second step includes a second judgment stepof judging whether touches have been constantly sensed, and a step ofproceeding to the third step in the case where the second judgment stepconfirms that touches have been constantly sensed. The third stepincludes a step of bringing the touch sensor into a resting state oroperating the touch sensor at a reduced drive frequency.

(4) Another embodiment of the present invention is a method foroperating an electronic device including a display device and a touchsensor. The display device includes a display portion and an illuminancesensor. The illuminance sensor has a function of measuring theilluminance of external light to divide the display portion into a firstregion which is not shaded and a second region which is shaded. Theluminance of an image displayed in the first region of the displayportion is increased. No image is displayed in the second region of thedisplay portion, or the luminance of an image displayed in the secondregion of the display portion is reduced.

(5) Another embodiment of the present invention is a method foroperating an electronic device including a display device and a touchsensor. The display device includes a display portion. The touch sensorhas a function of dividing the display portion into a first region inwhich no touch is sensed and a second region in which a touch is sensed.The luminance of an image displayed in the first region of the displayportion is increased. No image is displayed in the second region of thedisplay portion, or the luminance of an image displayed in the secondregion of the display portion is reduced.

(6) Another embodiment of the present invention is the operation methodaccording to any one of (1) to (5). In the operation method, the displaydevice includes a reflective liquid crystal element and either alight-emitting element or a transmissive liquid crystal element.

(7) Another embodiment of the present invention is the operation methodaccording to (6). In the operation method, the electronic device has afull-in-cell structure in which the reflective liquid crystal elementand the touch sensor share one electrode.

(8) Another embodiment of the present invention is the operation methodaccording to any one of (1) to (7). In the operation method, the displaydevice includes a transistor whose channel formation region includes ametal oxide.

(9) Another embodiment of the present invention is the operation methodaccording to any one of (1) to (8). In the operation method, the displaydevice includes a transistor whose channel formation region includessilicon.

According to one embodiment of the present invention, a novel displaydevice can be provided. According to another embodiment of the presentinvention, an electronic device including a novel display device can beprovided. According to another embodiment of the present invention, amethod for operating the display device or the electronic device can beprovided.

According to another embodiment of the present invention, a displaydevice with low power consumption can be provided. According to anotherembodiment of the present invention, a novel driving method for touchsensing can be provided.

Note that an effect of one embodiment of the present invention is notlimited to the above effects. The above effects do not preclude theexistence of other effects. The other effects are the ones that are notdescribed above and will be described below. The effects that are notdescribed above can be derived from the description of thespecification, the drawings, or the like by those skilled in the art.One embodiment of the present invention is to have at least one of theabove effects and the other effects. Therefore, one embodiment of thepresent invention does not necessarily have the above effects.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a configuration example of anelectronic device.

FIG. 2A illustrates an operation example of an electronic device in oneframe period, and FIG. 2B illustrates an example of the timing oftransition between a driving state and a resting state of the electronicdevice.

FIGS. 3A to 3D each illustrate an operation example of an electronicdevice in one frame period.

FIGS. 4A and 4B illustrate examples of the timing of transition betweena driving state and a resting state of an electronic device.

FIGS. 5A and 5B illustrate examples of the timing of transition betweena driving state and a resting state of an electronic device.

FIG. 6 is a block diagram illustrating a configuration example of anelectronic device.

FIG. 7 is a block diagram illustrating a configuration example of anelectronic device.

FIG. 8 illustrates an example of the timing of transition between adriving state and a resting state of an electronic device.

FIGS. 9A and 9B illustrate examples of the timing of transition betweena driving state and a resting state of an electronic device.

FIGS. 10A and 10B illustrate examples of the timing of transitionbetween a driving state and a resting state of an electronic device.

FIG. 11 is a flow chart illustrating an operation example of anelectronic device.

FIG. 12 is a flow chart illustrating an operation example of anelectronic device.

FIGS. 13A to 13D are schematic diagrams illustrating a configurationexample of a display device.

FIGS. 14A to 14D are circuit diagrams and timing charts illustrating aconfiguration example of a display device.

FIG. 15 is a perspective view illustrating an example of a displaydevice.

FIG. 16 is a cross-sectional view illustrating a structure example of aninput/output panel.

FIGS. 17A to 17D are cross-sectional views illustrating a structureexample of an input/output panel.

FIG. 18 is a cross-sectional view illustrating a structure example of atransistor included in an input/output panel.

FIG. 19 is a cross-sectional view illustrating an operation example of atouch sensor of an input/output panel.

FIGS. 20A and 20B are perspective views illustrating electronic devices.

FIG. 21 is a circuit block diagram illustrating a configuration exampleof a touch panel.

FIGS. 22A to 22C are a top view and perspective views illustrating aconfiguration example of a touch panel.

FIGS. 23A and 23B are a top view and a perspective view illustrating aconfiguration example of a touch panel.

FIGS. 24A to 24D are schematic cross-sectional views illustratingconfiguration examples of a touch sensor.

FIGS. 25A and 25B are schematic cross-sectional views illustratingconfiguration examples of a touch sensor.

FIGS. 26A and 26B are schematic cross-sectional views illustratingconfiguration examples of a touch sensor.

FIGS. 27A and 27B are schematic cross-sectional views illustratingconfiguration examples of a touch sensor.

FIGS. 28A to 28F are perspective views illustrating examples ofelectronic devices.

DETAILED DESCRIPTION OF THE INVENTION

In this specification, hybrid display (display in the third mode) refersto a method for displaying text and/or an image, in which reflectedlight and self-emitted light are used together in one panel tocomplement each other's color tone or light intensity. Alternatively,hybrid display refers to a method for displaying text and/or an imagewith the use of light from a plurality of display elements in one pixelor one sub-pixel. Note that a hybrid display device performing hybriddisplay may locally include a pixel or a sub-pixel performing displayusing one of a plurality of display elements and a pixel or a sub-pixelperforming display using two or more of the plurality of displayelements.

In this specification and the like, hybrid display satisfies at leastone of the above descriptions.

Furthermore, a hybrid display device includes a plurality of displayelements in one pixel or one sub-pixel. As an example of the pluralityof display elements, a reflective element that reflects light and aself-luminous element that emits light can be given. Note that thereflective element and the self-luminous element can be controlledindependently. The hybrid display device has a function of displayingtext and/or an image on a display portion with the use of reflectedlight and/or self-emitted light.

In this specification and the like, an “image” is a term including botha still image and a moving image. In other words, in this specificationand the like, an “image” can refer to either a still image or a movingimage. Furthermore, a “moving image” can refer to a video or the like.

In this specification and the like, a metal oxide means an oxide ofmetal in a broad sense. Metal oxides are classified into an oxideinsulator, an oxide conductor (including a transparent oxide conductor),an oxide semiconductor (also simply referred to as an OS), and the like.For example, a metal oxide used for an active layer of a transistor iscalled an oxide semiconductor in some cases. That is, a metal oxideincluded in a channel formation region of a transistor that has at leastone of an amplifying function, a rectifying function, and a switchingfunction can be referred to as a metal oxide semiconductor or shortly asan OS. Furthermore, an OS FET refers to a transistor including a metaloxide or an oxide semiconductor.

In this specification and the like, a metal oxide containing nitrogen isalso called a metal oxide in some cases. Moreover, a metal oxidecontaining nitrogen may be called a metal oxynitride.

Embodiment 1

In this embodiment, a display device, a touch sensor portion, and anoperation method thereof will be described.

Configuration Example

FIG. 1 is a block diagram illustrating a configuration example of anelectronic device described in this embodiment.

In this embodiment, an electronic device 100 is a hybrid display devicein which a common electrode of a reflective liquid crystal element isalso used as a touch sensor electrode of a touch sensor portion and anOS FET is used as a transistor included in a pixel circuit. Theelectronic device 100 includes a graphics processing unit GPU, a timingcontroller TC, a common electrode potential setting circuit CEPC, atouch panel controller TPC, a gate driver portion GD, a source driverportion SD, and a touch sensor display portion TDA.

The gate driver portion GD includes a first gate driver GD1 and a secondgate driver GD2. The source driver portion SD includes a first sourcedriver SD1 and a second source driver SD2. The touch sensor displayportion TDA includes a first display device DD1, a second display deviceDD2, and a touch sensor portion TSD. The first display device DD1includes a reflective liquid crystal element, and the second displaydevice DD2 includes either a light-emitting element or a transmissiveliquid crystal element.

The graphics processing unit GPU has a function of generating image databy rendering data 10 transmitted from the outside. Here, the term“outside” refers to a host device, a receiver, or the like provided inthe electronic device 100, for example. Furthermore, the graphicsprocessing unit GPU has a function of transmitting the image data to thetiming controller TC. Note that the electronic device 100 may include acentral processing unit (CPU) instead of the graphics processing unitGPU.

The timing controller TC has a function of scaling, in accordance withthe number of pixels in the first display device DD1 and/or the seconddisplay device DD2, the image data transmitted from the graphicsprocessing unit GPU. The scaled image data is transmitted to the sourcedriver portion SD. Furthermore, the timing controller TC has a functionof generating data control signals based on the image data transmittedfrom the graphics processing unit GPU. The data control signals aretransmitted to the source driver portion SD, the gate driver portion GD,and the common electrode potential setting circuit CEPC.

The common electrode potential setting circuit CEPC has functions ofswitching the polarity of the reflective liquid crystal included in thepixel circuit and changing a potential applied to the common electrode(touch sensor electrode), in response to the data control signaltransmitted from the timing controller TC. Specifically, in thisspecification and the like, the function of changing a potential appliedto the common electrode (touch sensor electrode) refers to switchingbetween a step of inputting a common potential to the common electrode(touch sensor electrode) to drive the first display device DD1 and astep of inputting a pulse signal for the touch sensor to the commonelectrode (touch sensor electrode) to make the touch sensor portion TSDperform a sensing operation.

The gate driver portion GD has a function of transmitting, in responseto the data control signal transmitted from the timing controller TC,selection signals of the display elements to the first display deviceDD1 and the second display device DD2 at a drive frequency based on thedata control signal. Specifically, a selection signal from the firstgate driver GD1 is transmitted to the first display device DD1 as asignal for selecting the reflective liquid crystal element, and aselection signal from the second gate driver GD2 is transmitted to thesecond display device DD2 as a signal for selecting thelight-transmitting element (transmissive liquid crystal element).Depending on the data control signal, the gate driver portion GD can bebrought into a resting state.

The source driver portion SD has a function of transmitting the scaledimage data (hereinafter referred to as an image signal) transmitted fromthe timing controller TC, to the first display device DD1. The imagesignal is transmitted at a drive frequency based on the data controlsignal which is also transmitted from the timing controller TC.Specifically, an image signal from the first source driver SD1 istransmitted to the first display device DD1 as image data displayed bythe reflective liquid crystal element, and an image signal from thesecond source driver SD2 is transmitted to the second display device DD2as image data displayed by the light-transmitting element (transmissiveliquid crystal element). Depending on the data control signal, thesource driver portion SD can be brought into a resting state.

Note that the first display device DD1 and the second display device DD2may have the same drive frequency or different drive frequencies.

The touch panel controller TPC receives the data control signal from thetiming controller TC and thus can make the touch sensor portion TSDperform the sensing operation at a drive frequency based on the datacontrol signal. Depending on the data control signal, the touch sensorportion TSD can be brought into a resting state. Furthermore, the touchpanel controller TPC has a function of controlling a touch sensor driverand a sensing circuit which are included in the touch sensor portionTSD. A signal which includes touch information sensed by the sensingcircuit is processed by the touch panel controller TPC and transmittedto a main computer such as a host device.

In a block diagram in this specification and the like, components arefunctionally classified and shown by blocks that are independent fromeach other. However, in an actual circuit or the like, such componentsare sometimes hard to classify functionally, and there is a case whereone circuit is responsible for a plurality of functions or a case wherea plurality of circuits are responsible for one function. Therefore,blocks illustrated in a block diagram do not necessarily show componentsdescribed in the specification, which can be explained with another termas appropriate depending on the situation.

For example, in the electronic device 100 in FIG. 1, the first displaydevice DD1 and the touch sensor portion TSD are separately illustrated.However, since the common electrode of the liquid crystal element isalso used as the touch sensor electrode of the touch sensor portion, thecommon electrode (touch sensor electrode) is a common component sharedby the first display device DD1 and the touch sensor portion TSD inFIG. 1. Accordingly, the expression “the first display device DD1includes a common electrode (touch sensor electrode)” can be replacedwith the expression “the touch sensor portion TSD includes a commonelectrode (touch sensor electrode).

Although FIG. 1 illustrates an example in which the electronic device100 is a hybrid display device and thus includes the second displaydevice DD2, one embodiment of the present invention is not limited tothe hybrid display device. In this sense, one embodiment of the presentinvention may be the electronic device 100 which does not include thesecond display device DD2, the second gate driver, and the second sourcedriver and is provided with the touch sensor display portion TDAincluding only the first display device DD1 and the touch sensor portionTSD.

Operation Example 1

Next, a method for driving the electronic device 100 will be described.

FIGS. 2A and 2B schematically illustrate examples of the timing ofwriting image data to the first display device DD1 and/or the seconddisplay device DD2 and the timing of sensing of the touch sensor portionTSD. In FIG. 2A, one frame period includes an image writing period PWD,a sensing period SP1, and a sensing period SP2. As illustrated in FIG.2A, writing of image data to the first display device DD1 and/or thesecond display device DD2 and sensing of the touch sensor portion areperformed in one frame period. Note that one frame period is 1/60 s.

The image writing period PWD is a period in which image data is writtento the display elements of the first display device DD1 and/or thesecond display device DD2, and accounts for ½ ( 1/120 s) of one frameperiod. In the full-in-cell structure in which the common electrode isused as a touch sensor electrode, a common potential is applied to thecommon electrode (touch sensor electrode) of the liquid crystal elementand image data is written to the liquid crystal element in the imagewriting period PWD. Meanwhile, the touch sensor portion is not availablefor sensing and thus in the resting state.

Each of the sensing periods SP1 and SP2 is a period in which the touchsensor portion TSD of the electronic device 100 performs a sensingoperation, and accounts for ¼ ( 1/240 s) of one frame period. That is,in FIG. 2A, the sensing operation is performed twice in one frameperiod. In the full-in-cell structure in which the common electrode isused as a touch sensor electrode, a touch sensing pulse signal isapplied to the common electrode (touch sensor electrode) of the liquidcrystal element and the touch sensor is driven in the sensing period SP1and the sensing period SP2. Meanwhile, the liquid crystal element of thefirst display device DD1 retains the data written previously, and thus,writing is not performed. In other words, a selection signal does notneed to be transmitted to the liquid crystal element; therefore, thegate driver for the first display device DD1 and/or the gate driver forthe second display device DD2 are in the resting (non-scanning) state.

In the full-in-cell touch sensor display portion TDA, in the case whereno image is displayed on the first display device DD1 and an image isdisplayed on the second display device DD2 (second mode), the firstdisplay device DD1 is in the resting (non-scanning) state also in theimage writing period PWD. In the full-in-cell touch sensor displayportion TDA, in the case where no image is displayed on the seconddisplay device DD2 and an image is displayed on the first display deviceDD1 (first mode), the second display device DD2 is in the resting(non-scanning) state also in the image writing period PWD

FIG. 2B illustrates examples of the driving state, the resting state,and the state transition timing of the first display device DD1 and/orthe second display device DD2 and the touch sensor portion TSD which aredriven in accordance with the timing chart of one frame period in FIG.2A.

As illustrated in FIG. 2B, one frame period lasts from Time T1 to TimeT2, and the image writing operation of the first display device DD1and/or the second display device DD2 is performed once in every frameperiod. During the writing operation (image writing period PWD), thetouch sensor portion TSD is in the resting state. After the imagewriting operation of the first display device DD1 and/or the seconddisplay device DD2 is terminated, the first display device DD1 and/orthe second display device DD2 transition from the driving state to theresting state.

When the first display device DD1 and/or the second display device DD2are brought into the resting state, the touch sensor portion TSDtransitions from the resting state to the driving state. At this time,the touch sensor portion performs a sensing operation in the sensingperiod SP1 and the sensing period SP2. After the sensing operation isterminated, the touch sensor portion TSD transitions from the drivingstate to the resting state. At this time, the first display device DD1and/or the second display device DD2 transition from the resting stateto the driving state.

At Time T2, the driving in one frame period including the aboveoperations is terminated. In FIG. 2B, after Time T2, the driving in oneframe period illustrated in FIG. 2A is repeated in a manner similar tothat of the operations from Time T1 to Time T2. Note that in FIG. 2B,operations in one frame period are performed from Time T2 to Time T3.

The timing illustrated in FIG. 2A is set on the assumption of a4.91-inch display device with 1280×720 pixels (HD). The lengths of theimage writing period PWD, the sensing period SP1, and the sensing periodSP2 may be changed depending on the size of the touch sensor displayportion TDA, namely the number of pixels in the first display device DD1and the second display device DD2 or the size of the touch sensorportion TSD.

FIGS. 3A to 3D illustrate examples of the operation timing of theelectronic device 100 in one frame period, which are different from theexamples in FIGS. 2A and 2B.

In FIG. 3A, one frame period includes an image writing period PWD and asensing period SP3. The image writing period PWD in FIG. 3A accounts for½ ( 1/120 s) of one frame period, and the sensing period SP3 in FIG. 3Aaccounts for ½ ( 1/120 s) of one frame period. In the sensing period SP3in FIG. 3A, the sensing operation is performed once. That is, the numberof sensing operations in the timing chart in FIG. 3A is smaller thanthat in the timing chart in FIG. 2A. When the reduction in the number ofsensing operations does not affect the sensitivity of the touch sensorportion TSD, the operation timing in FIG. 3A with a smaller number ofsensing operations enables lower power consumption of the touch sensorportion TSD than the operation timing in FIG. 2A.

In FIG. 3B, one frame period includes an image writing period PWD and asensing period SP3. The image writing period PWD in FIG. 3B accounts for¾ ( 1/80 s) of one frame period, and the sensing period SP3 in FIG. 3Baccounts for ¼ ( 1/240 s) of one frame period. In the sensing period SP3in FIG. 3B, the sensing operation is performed once. That is, the imagewriting period PWD in the timing chart in FIG. 3B is longer than that inthe timing chart in FIG. 2A; therefore, the operation timing in FIG. 3Bis suitable for a display device with a larger number of pixels and/or alarger size.

In FIG. 3C, one frame period includes an image writing period PWD and asensing period SP3. The image writing period PWD in FIG. 3C accounts for¼ ( 1/240 s) of one frame period, and the sensing period SP3 in FIG. 3Caccounts for ¾ ( 1/80 s) of one frame period. In the sensing period SP3in FIG. 3C, the sensing operation is performed once. That is, the imagewriting period PWD in the timing chart in FIG. 3C is shorter than thatin the timing chart in FIG. 2A; therefore, the operation timing in FIG.3C is suitable for a display device with a smaller number of pixelsand/or a smaller size.

In FIG. 3D, one frame period includes an image writing period PWD and asensing period SP3. In FIG. 3D, the sum of the length of the imagewriting period PWD and the length of the sensing period SP3 in one frameperiod is 1/60 s; however, there is no limitation on the length of theimage writing period PWD and the length of the sensing period SP3. Thesensing period SP3 in FIG. 3D includes a plurality of sensing periodsSP, and the sensing operation is performed once in every sensing periodSP. In other words, in the operation timing chart in FIG. 3D, aplurality of sensing operations is performed in one frame period, whichis a suitable method for the improvement in the sensitivity of the touchsensor portion TSD. Note that one frame period in FIG. 2A corresponds tothat in FIG. 3D, when the number of sensing periods SP in one frameperiod is set to two and the lengths of the image writing period PWD andthe sensing period SP3 are each set to 1/120 s.

Operations in one frame period of one embodiment of the presentinvention are not limited to the examples of the operations in one frameperiod in FIGS. 3A to 3D. For example, in one frame period of oneembodiment of the present invention, the sensing period SP3 may comefirst and be followed by the image writing period PWD.

Operation Example 2

FIG. 4A illustrates examples that are different from those in FIG. 2B,namely examples of the driving state, the resting state, and the statetransition timing of the first display device DD1 and/or the seconddisplay device DD2 and the touch sensor portion TSD in the electronicdevice 100. Note that the operation timing in one frame period in FIG.4A corresponds to any one of the operation timings in FIGS. 3A to 3D; inaccordance with this timing, the normal operation of the electronicdevice 100 is performed.

As illustrated in FIG. 4A, one frame period lasts from Time T1 to TimeT2, and the image writing operation of the first display device DD1and/or the second display device DD2 is performed once in the one frameperiod. During the writing operation (image writing period PWD), thetouch sensor portion TSD is in the resting state. After the imagewriting operation of the first display device DD1 and/or the seconddisplay device DD2 is terminated, the first display device DD1 and/orthe second display device DD2 transition from the driving state to theresting state.

When the first display device DD1 and/or the second display device DD2are brought into the resting state, the touch sensor portion TSDtransitions from the resting state to the driving state. At this time,the touch sensor portion performs a sensing operation in the sensingperiod SP3. At Time T2, i.e., after the termination of the sensingoperation, the touch sensor portion TSD transitions from the drivingstate to the resting state. At this time, the first display device DD1and/or the second display device DD2 transition from the resting stateto the driving state.

In the case where no operation by the user, i.e. no touch, is sensed fora certain period until Time T2, the touch sensor portion TSD is broughtinto the resting state at Time T2 regardless of the operation timing inone frame period. Note that the length of the period in which the touchsensor portion TSD is in the resting state may be arbitrarily determinedby the user or preset in the electronic device 100, for example. In FIG.4A, the touch sensor portion TSD keeps the resting state for three frameperiods (from Time T2 to Time T3). In this specification, a long restingstate of the touch sensor portion TSD, such as the above-mentioned statein the period from Time T2 to Time T3 is referred to as a long suspendedmode.

Strictly speaking, the resting state of the touch sensor portion TSDdoes not end at Time T3. From Time T3, the operation in any one of thetiming charts in FIGS. 3A to 3D is performed; therefore, the restingstate of the touch sensor portion TSD does not end at Time T3 and lastsuntil the termination of the image writing period PWD starting at TimeT3 (until Time T4). Thus, in this specification, not only the state inthe period from Time T2 to Time T3 but also the state in the period fromTime T2 to Time T4 can be referred to as a long suspended mode.

After Time T3, the operations in the normal one frame period arerepeated in a manner similar to that in FIG. 2B. In the case where nooperation by the user, i.e. no touch, is sensed for a certain period,the touch sensor portion TSD transitions to the long suspended mode asin the period from Time T2 to Time T3.

In FIG. 4A, the touch sensor portion TSD is in the long suspended modefrom Time T2 to Time T4; however, the operation timing of one embodimentof the present invention is not limited thereto. For example, asillustrated in FIG. 4B, in the middle of the period in the longsuspended mode, the touch sensor portion TSD may operate on the basis ofthe operation timing in the normal one frame period. In FIG. 4B, thetouch sensor portion TSD is in the long suspended mode from Time T2 toTime T2-1.5, operates on the basis of the operation timing in the normalone frame period from Time T2-1 to Time T2-2, and is again in the longsuspended mode from Time T2-2 to Time T3-1. In FIG. 4B, from Time T2 toTime T4, the touch sensor portion TSD has one sensing period per twoframe periods (one sensing operation every 1/30 s), i.e. operates at adrive frequency of 30 Hz. Depending on circumstances or situation, thetouch sensor portion TSD may operate at a drive frequency that is lowerthan 60 Hz and is not 30 Hz. In this specification, the operation at alow drive frequency is referred to as idling stop (IDS) driving. Notethat the IDS driving of a display device will be described in detail inEmbodiment 4.

Operation Example 3

FIG. 5A illustrates examples that are different from those in FIG. 2Band FIGS. 4A and 4B, namely examples of the driving state, the restingstate, and the state transition timing of the first display device DD1and/or the second display device DD2 and the touch sensor portion TSD inthe electronic device 100. Note that the operation timing in one frameperiod in FIG. 5A corresponds to any one of the operation timings inFIGS. 3A to 3D.

As illustrated in FIG. 5A, one frame period lasts from Time T1 to TimeT2, and the image writing operation of the first display device DD1and/or the second display device DD2 is performed once in the one frameperiod. During the writing operation (image writing period PWD), thetouch sensor portion TSD is in the resting state. After the imagewriting operation of the first display device DD1 and/or the seconddisplay device DD2 is terminated, the first display device DD1 and/orthe second display device DD2 transition from the driving state to theresting state.

When the first display device DD1 and/or the second display device DD2are brought into the resting state, the touch sensor portion TSDtransitions from the resting state to the driving state. At this time,the touch sensor portion performs a sensing operation in the sensingperiod SP3. At Time T2, i.e., after the termination of the sensingoperation, the touch sensor portion TSD transitions from the drivingstate to the resting state.

Here, the following case will be described: the touch sensor portion TSDtransitions to the long suspended mode when operations by the user, i.e.touches, are constantly sensed until Time T2 and the first displaydevice DD1 and/or the second display device DD2 are brought into thelong resting state from Time T2. For example, the long resting state ofthe first display device DD1 and/or the second display device DD2 can betriggered when the graphics processing unit GPU of the electronic device100 illustrated in FIG. 1 compares the previous frame with the presentframe and finds no difference in grayscale or color tone in every pixel.In FIG. 5A, the first display device DD1 and/or the second displaydevice DD2 are in the long resting state from Time T2 to Time T4.

The operation of the touch sensor portion TSD transitions to the longsuspended mode after the first display device DD1 and/or the seconddisplay device DD2 are brought into the long resting state. In FIG. 5A,the long suspended mode lasts from Time T3 to Time T5.

After Time T4, the operations in one frame period are repeated in amanner similar to that in FIG. 2B. In the case where operations by theuser, i.e. touches, are constantly sensed and the first display deviceDD1 and/or the second display device DD2 are brought into the longresting state, the touch sensor portion TSD transitions to the longsuspended mode as in the period from Time T3 to Time T5.

In FIG. 5A, the first display device DD1 and/or the second displaydevice DD2 are in the long resting state from Time T2 to Time T4;however, the operation timing of one embodiment of the present inventionis not limited thereto. As illustrated in FIG. 5B, for example, withoutbringing the first display device DD1 and/or the second display deviceDD2 into the long resting state, image rewriting may be performed at areduced frequency when the touch sensor portion TSD is in the longsuspended mode. In FIG. 5B, from Time T3 to Time T4, the first displaydevice DD1 and/or the second display device DD2 have one image writingperiod per two frame periods (one writing every 1/30 s), i.e. operate ata drive frequency of 30 Hz. Depending on circumstances or situation, thefirst display device DD1 and/or the second display device DD2 mayoperate at a drive frequency that is lower than 60 Hz and is not 30 Hz.That is, the IDS driving of the first display device DD1 and/or thesecond display device DD2 may be performed at a reduced drive frequency.The IDS driving of a display device will be described in detail inEmbodiment 4.

The above-described operation method in FIG. 5B is effective in the casewhere the touch sensor portion TSD is in the long suspended mode for along time. Since image data retained in display pixels of the firstdisplay device DD1 and/or the second display device DD2 is regularlyrefreshed, the display quality of the touch sensor display portion TDAcan be improved.

As an example of the case where operations by the user, i.e. touches,are constantly sensed and the first display device DD1 and/or the seconddisplay device DD2 are brought into the resting state (or the IDSdriving is performed) from Time T2, the case where the user keepstouching the display screen and a displayed image does not change can beassumed. Examples of an application that satisfies this assumptioninclude e-book reader software, a browser, moving image reproductionsoftware, and a file browser.

While the user is running any of the above applications in theelectronic device 100, the user may keep touching the touch sensordisplay portion TDA with a finger to operate the electronic device 100quickly. For example, while the user performs a touch operation toscroll an image displayed on a browser running as an application, thetouch operation may be temporarily stopped in the state in which thefinger touches the touch sensor display portion TDA and the scroll ofthe displayed image may be paused. In this case, with the fingertouching the touch sensor display portion TDA, the user browses thedisplayed image with the scroll paused. After finishing browsing thedisplayed image, the user moves the finger which has touched the touchsensor display portion TDA again and scrolls the displayed image. Inthis manner, in the case where the user temporarily pauses a touchoperation of the electronic device 100 with a finger touching the touchsensor display portion TDA and browses a displayed image, the electronicdevice 100 preferably operates in the manner described in OperationExample 3.

The touch sensor portion TSD continues the sensing operation during thetouch operation such as the scroll of the display screen. When the usertemporarily pauses the touch operation with the finger touching thetouch sensor display portion TDA and browses the displayed image, thedisplayed image does not change. Therefore, the first display device DD1and/or the second display device DD2 are brought into the resting state(or the IDS driving is performed). At this time, even though the fingertouches the touch sensor display portion TDA, this touch is not regardedas an input to the electronic device 100; therefore, the touch sensorportion TSD preferably operates in the long suspended mode (or theidling stop driving is preferably performed).

The power consumption for the sensing operation in the electronic device100 can be reduced by applying Operation Examples 1 to 3 to theoperation of the electronic device 100.

This embodiment can be combined with any of the other embodiments inthis specification as appropriate.

Embodiment 2

In this embodiment, a display device and a touch sensor portion whichare different from those in Embodiment 1 and an operation method thereofwill be described.

Configuration Example 1

FIG. 6 is a block diagram illustrating a configuration example of anelectronic device described in this embodiment.

An electronic device 101 is an electronic device which includes a firstdisplay device DD1 including a reflective liquid crystal element (or atransmissive liquid crystal element; hereinafter, the general term“liquid crystal element” will be used) and in which an OS FET is used asa transistor included in a pixel circuit. Note that unlike in Embodiment1, a common electrode of the liquid crystal element and a touch sensorelectrode in a touch sensor portion are separately provided. Theelectronic device 101 includes a graphics processing unit GPU, a timingcontroller TC, a touch panel controller TPC, a first gate driver GD1, afirst source driver SD1, and a touch sensor display portion TDA.

The electronic device 101 has a configuration corresponding to that ofthe electronic device 100 in Embodiment 1 which does not include thesecond display device DD2, the second gate driver GD2, the second sourcedriver SD2, and the common electrode potential setting circuit CEPC.Therefore, the description of the electronic device 100 can be referredto for the electrical connection in the electronic device 101. In theelectronic device 101 illustrated in FIG. 6, the first gate driver GD1and the first source driver SD1 represent a gate driver portion GD and asource driver portion SD, respectively.

The description of the graphics processing unit GPU in Embodiment 1 canbe referred to for the graphics processing unit GPU here.

The timing controller TC has a function of scaling, in accordance withthe number of pixels in the first display device DD1, image datatransmitted from the graphics processing unit GPU. The scaled image datais transmitted to the first source driver SD1. Furthermore, the timingcontroller TC has a function of generating data control signals based onthe image data transmitted from the graphics processing unit GPU. Thedata control signals are transmitted to the first source driver SD1 andthe first gate driver GD1.

The first gate driver GD1 has a function of transmitting, in response tothe data control signal transmitted from the timing controller TC, aselection signal of a display element to the first display device DD1 ata drive frequency based on the data control signal. Specifically, aselection signal from the first gate driver GD1 is transmitted to thefirst display device DD1 as a signal for selecting the liquid crystalelement. Depending on the data control signal, the first gate driver GD1can be brought into a resting state.

The first source driver SD1 has a function of transmitting the scaledimage data (hereinafter referred to as an image signal) transmitted fromthe timing controller TC to the first display device DD1. The imagesignal is transmitted at a drive frequency based on the data controlsignal which is also transmitted from the timing controller TC.Specifically, an image signal from the first source driver SD1 istransmitted to the first display device DD1 as image data displayed bythe liquid crystal element. Depending on the data control signal, thefirst source driver SD1 can be brought into a resting state.

The description of the touch panel controller TPC in Embodiment 1 can bereferred to for the touch panel controller TPC here.

Configuration Example 2

FIG. 7 is a block diagram illustrating a configuration example of anelectronic device that is different from the electronic device 100described in Embodiment 1 and the electronic device 101 described inConfiguration Example 1 of this embodiment.

An electronic device 102 is an electronic device which includes a seconddisplay device DD2 including a light-emitting element and in which an OSFET is used as a transistor included in a pixel circuit. The electronicdevice 102 includes a graphics processing unit GPU, a timing controllerTC, a touch panel controller TPC, a second gate driver GD2, a secondsource driver SD2, and a touch sensor display portion TDA.

The electronic device 102 has a configuration corresponding to that ofthe electronic device 100 in Embodiment 1 which does not include thefirst display device DD1, the first gate driver GD1, the first sourcedriver SD1, and the common electrode potential setting circuit CEPC.Therefore, the description of the electronic device 100 can be referredto for the electrical connection in the electronic device 102. In theelectronic device 102 illustrated in FIG. 7, the second gate driver GD2and the second source driver SD2 represent a gate driver portion GD anda source driver portion SD, respectively.

The description of the graphics processing unit GPU in Embodiment 1 canbe referred to for the graphics processing unit GPU here.

The timing controller TC has a function of scaling, in accordance withthe number of pixels in the second display device DD2, image datatransmitted from the graphics processing unit GPU. The scaled image datais transmitted to the second source driver SD2. Furthermore, the timingcontroller TC has a function of generating data control signals based onthe image data transmitted from the graphics processing unit GPU. Thedata control signals are transmitted to the second source driver SD2 andthe second gate driver GD2.

The second gate driver GD2 has a function of transmitting, in responseto the data control signal transmitted from the timing controller TC, aselection signal of a display element to the second display device DD2at a drive frequency based on the data control signal. Specifically, aselection signal from the second gate driver GD2 is transmitted to thesecond display device DD2 as a signal for selecting the light-emittingelement. Depending on the data control signal, the second gate driverGD2 can be brought into a resting state.

The second source driver SD2 has a function of transmitting the scaledimage data (hereinafter referred to as an image signal) transmitted fromthe timing controller TC to the second display device DD2. The imagesignal is transmitted at a drive frequency based on the data controlsignal which is also transmitted from the timing controller TC.Specifically, an image signal from the second source driver SD2 istransmitted to the second display device DD2 as image data displayed bythe light-emitting element. Depending on the data control signal, thesecond source driver SD2 can be brought into a resting state.

The description of the touch panel controller TPC in Embodiment 1 can bereferred to for the touch panel controller TPC here.

Operation Example 1

FIG. 8 illustrates an example of the timing for driving the displaydevice (the first display device DD1 or the second display device DD2)and the touch sensor portion TSD which are included in the touch sensordisplay portion TDA of the electronic device 101 or the electronicdevice 102.

In the timing chart in FIG. 8, an image writing period PWD for one framein the first display device DD1 or the second display device DD2 lastsfrom Time T1 to Time T2, and a sensing operation for one frame in thetouch sensor portion TSD lasts from Time T1 to Time T3.

In the timing chart in FIG. 8, the first display device DD1 or thesecond display device DD2 and the touch sensor portion TSD each repeatthe operation in one frame period without being brought into the restingstate.

Note that in FIG. 8, the length of one frame period in which the firstdisplay device DD1 or the second display device DD2 is driven isdifferent from the length of one frame period in which the touch sensorportion TSD is driven; however, these lengths may be equal to eachother.

Operation Example 2

Next, the following case will be described: when no operation by theuser, i.e. no touch, is sensed for a certain period, the touch sensorportion TSD driven on the basis of the timing in FIG. 8 transitions tothe resting state (long suspended mode).

FIG. 9A illustrates an example of the timing at which the touch sensorportion TSD transitions from the driving state to the long suspendedmode in the case where no touch is sensed by the touch sensor portionTSD driven on the basis of the timing in FIG. 8.

In the examples of the driving timing illustrated in FIG. 8 and FIG. 9A,the touch sensor portion TSD performs the sensing operation once in oneframe period. In FIG. 9A, the sensing operation is performed twice in aperiod from Time T1 to Time T4.

At this time, in the case where no operation by the user, i.e. no touch,is sensed for a certain period until Time T4, the touch sensor portionTSD transitions from the driving state to the long suspended mode atTime T4. Note that the length of the period in which the touch sensorportion TSD is in the long suspended mode may be arbitrarily determinedby the user or preset in the electronic device 101 or the electronicdevice 102, for example. In FIG. 9A, the touch sensor portion TSD is inthe long suspended mode from Time T4 to Time T5.

After Time T5, the touch sensor portion TSD repeats the operation in oneframe period as in FIG. 8. In the case where no operation by the user,i.e. no touch, is sensed for a certain period, the touch sensor portionTSD transitions to the long suspended mode as in the period from Time T4to Time T5 in FIG. 9A.

In FIG. 9A, the touch sensor portion TSD keeps the resting state for along time from Time T4 to Time T5; however, the operation timing of oneembodiment of the present invention is not limited thereto. For example,as illustrated in FIG. 9B, in the case where no operation by the user,i.e. no touch, is sensed for a certain period until Time T4, the touchsensor portion TSD may alternate between the resting state (or the longsuspended mode) and the sensing operation after Time T4. That is, inFIG. 9B, the drive frequency of the sensing operation of the touchsensor portion TSD after Time T4 is lower than the drive frequency ofthe sensing operation before Time T4. In Operation Example 3 inEmbodiment 1, the IDS driving of the first display device DD1 and/or thesecond display device DD2 is performed; in this operation example, theIDS driving of the touch sensor portion TSD is performed.

Operation Example 3

Next, the following case will be described: when operations by the user,i.e. touches, are constantly sensed and the IDS driving of the firstdisplay device DD1 or the second display device DD2 starts at Time T4,the touch sensor portion TSD driven on the basis of the timing in FIG. 8transitions to the resting state (long suspended mode).

In the examples of the driving timing illustrated in FIG. 8 and FIG.10A, the touch sensor portion TSD performs the sensing operation once inone frame period. In FIG. 10A, the sensing operation is performed threetimes in a period from Time T1 to Time T5.

Here, the following case will be described: when operations by the user,i.e. touches, are constantly sensed until Time T3 and the IDS driving ofthe first display device DD1 or the second display device DD2 starts atTime T4, the touch sensor portion TSD transitions to the long suspendedmode. For example, the IDS driving of the first display device DD1 orthe second display device DD2 can be triggered when the graphicsprocessing unit GPU of the electronic device 101 illustrated in FIG. 6or the electronic device 102 illustrated in FIG. 7 compares the previousframe with the present frame and finds no difference in grayscale orcolor tone in every pixel. In FIG. 10A, the IDS driving of the firstdisplay device DD1 or the second display device DD2 is performed fromTime T4 to Time T7.

The operation of the touch sensor portion TSD transitions to the restingstate (long suspended mode) after the IDS driving of the first displaydevice DD1 or the second display device DD2 starts. In FIG. 10A, theresting state (long suspended mode) lasts from Time T5 to Time T6.

After Time T6, the touch sensor portion TSD repeats the operation in oneframe period as in FIG. 8. In the case where operations by the user,i.e. touches, are constantly sensed and the IDS driving of the firstdisplay device DD1 or the second display device DD2 starts, the touchsensor portion TSD transitions to the long suspended mode as in theperiod from Time T5 to Time T6.

In FIG. 10A, the IDS driving of the first display device DD1 or thesecond display device DD2 is performed from Time T4 to Time T7; however,the operation timing of one embodiment of the present invention is notlimited thereto. As illustrated in FIG. 10B, for example, it issometimes possible not to perform image rewriting at all when the touchsensor portion TSD is in the long suspended mode, without performing theIDS driving of the first display device DD1 or the second display deviceDD2. That is, the first display device DD1 or the second display deviceDD2 may be in the resting state in that period. This operation method iseffective in the case where the display element included in the firstdisplay device DD1 or the second display device DD2 can retain imagedata for a long time. In FIG. 10B, the first display device DD1 or thesecond display device DD2 is in the resting state from Time T4 to TimeT7.

Like Operation Example 3 in Embodiment 1, this operation example iseffectively used for, for example, applications in which operations bythe user, i.e. touches, are constantly sensed and a displayed image doesnot change, such as e-book reader software, a browser, moving imagereproduction software, and a file browser.

The power consumption for the sensing operation in the electronic device101 or the electronic device 102 can be reduced by applying OperationExamples 1 to 3 to the operation of the electronic device 101 or theelectronic device 102.

Note that the operation examples of the electronic device 101 and theelectronic device 102 are described in this embodiment; however, theoperation examples of this embodiment can also be applied to an on-cellelectronic device including a hybrid display device and a touch sensor.

This embodiment can be combined with any of the other embodiments inthis specification as appropriate.

Embodiment 3

The operation examples described in Embodiments 1 and 2 are summarizedin flow charts in FIG. 11 and FIG. 12.

A method for driving any of the electronic devices 100 to 102 includesSteps ST1 to ST7. In this embodiment, the general term “electronicdevice” is used for the electronic devices 100 to 102, and the generalterm “display device” is used for the first display device DD1 and thesecond display device DD2 which are included in the electronic device.

Step ST1 includes a step in which the electronic device is driven. Here,the first display device DD1 and/or the second display device DD2 aredriven in a normal driving state, and the touch sensor portion TSD is ina normal driving state. After Step ST1 is terminated, the processproceeds to Step ST2.

In Step ST2, whether no touch has been sensed by the touch sensorportion TSD for a certain period is judged. Here, as mentioned in theabove embodiment, the certain period refers to time that is arbitrarilydetermined by the user, time that is preset in the electronic device, orthe like. In the case where a touch has been sensed, the processproceeds to “A” in FIG. 11; in the case where no touch has been sensed,the process proceeds to Step ST3.

In Step ST3, whether the long resting state or the IDS driving of thedisplay device has started is judged. As described in the aboveembodiment, the long resting state or the IDS driving of the displaydevice can be triggered when the graphics processing unit GPU includedin the electronic device compares the previous frame with the presentframe and finds no difference in grayscale or color tone in every pixel.In the case where the long resting state or the IDS driving of thedisplay device has started, the process proceeds to Step ST4; in thecase where the long resting state or the IDS driving of the displaydevice has not started, the process proceeds to Step ST2.

In Step ST4, whether touches have been constantly sensed by the touchsensor portion TSD since before the long resting state or the IDSdriving of the display device starts. In the case where touches havebeen constantly sensed, the process proceeds to “A” in FIG. 11; in thecase where no constant touch has been sensed, the process proceeds toStep ST5.

Step ST5 includes a step in which the display device returns from thelong resting state or the IDS driving to the normal driving state. AfterStep ST5 is terminated, the process proceeds to Step ST2.

“A” in FIG. 11 means that the process proceeds to Step ST6 in FIG. 12.

Step ST6 includes a step in which the long suspended mode (or the IDSdriving) of the touch sensor portion TSD starts. After Step ST6 isterminated, the process proceeds to Step ST7.

Step ST7 includes a step in which the touch sensor portion TSD returnsfrom the long suspended mode (or the IDS driving) to the normal driving.After Step ST7 is terminated, the process proceeds to “B” in FIG. 12.

“B” in FIG. 12 means that the process proceeds to Step ST2 in FIG. 11.

In a flow chart in this specification and the like, the whole operationmethod is divided into a plurality of operations corresponding to stepsthat are independent of each other. However, it is difficult to dividean actual operation method into a plurality of operations; a pluralityof operations may relate to one step, or one operation may relate to aplurality of steps. Thus, steps in a flow chart are not limited tooperations described in the specification, and the steps can beexpressed in a different way depending on the situation.

This embodiment can be combined with any of the other embodiments inthis specification as appropriate.

Embodiment 4

In this embodiment, a display device which can be used for theelectronic device 100 described in the above embodiment and electronicdevices 5200A and 5200B described in Embodiment 5 will be described withreference to FIGS. 13A to 13D, FIGS. 14A to 14D, FIG. 15, FIG. 16, FIGS.17A to 17D, FIG. 18, and FIG. 19. The display device of this embodimentincludes a first display element that reflects visible light and asecond display element that emits visible light.

For example, the first display device DD1 includes a matrix of firstdisplay elements, and the second display device DD2 includes a matrix ofsecond display elements.

The display device of this embodiment has a function of displaying animage with the use of light reflected from the first display elementand/or light emitted from the second display element.

As the first display element, an element which displays an image byreflecting external light can be used. Such an element does not includea light source; thus, power consumption for display can be significantlyreduced.

As the first display element, typically, a reflective liquid crystalelement can be used. Alternatively, as the first display element, amicroelectromechanical systems (MEMS) shutter element, an opticalinterference type MEMS element, an element to which a microcapsulemethod, an electrophoretic method, an electrowetting method, or the likeis applied, or the like can be used.

As the second display element, a light-emitting element is preferablyused. Since the luminance and chromaticity of light emitted from such adisplay element are less affected by external light, a clear image thathas high color reproducibility (wide color gamut) and a high contrastcan be displayed.

As the second display element, a self-luminous light-emitting elementsuch as an organic light-emitting diode (OLED), a light-emitting diode(LED), a quantum-dot light-emitting diode (QLED), or a semiconductorlaser can be used. Although a self-luminous light-emitting element ispreferably used as the second display element, the second displayelement is not limited thereto; for example, a transmissive liquidcrystal element which is combined with a light source such as abacklight or a sidelight may be used.

The display device of this embodiment has a first mode in which an imageis displayed using the first display element, a second mode in which animage is displayed using the second display element, and a third mode inwhich an image is displayed using both the first display element and thesecond display element. The first to third modes can be switchedautomatically or manually. The first to third modes will be described indetail below.

[First Mode]

In the first mode, an image is displayed using the first display elementand external light. Since a light source is unnecessary in the firstmode, power consumed in this drive mode is extremely low. Whensufficient external light enters the display device (e.g., in a brightenvironment), for example, an image can be displayed using lightreflected from the first display element. For example, the first mode iseffective in the case where external light is white or near-white lightwith sufficient intensity. The first mode is suitable for displayingtext. Furthermore, the use of reflected external light enableseye-friendly display in the first mode, which leads to an effect ofreducing eyestrain. Note that the first mode may be referred to asreflective display mode (reflection mode) because display is performedusing reflected light.

[Second Mode]

In the second mode, an image is displayed utilizing light emitted fromthe second display element. Thus, an extremely clear image (with highcontrast and high color reproducibility) can be displayed regardless ofthe illuminance and chromaticity of external light. For example, thesecond mode is effective in the case where the illuminance is extremelylow, e.g., during the night or in a dark room. When a bright image isdisplayed in a dark environment, a user may feel that the image is toobright. To prevent this, an image with reduced luminance is preferablydisplayed in the second mode. Thus, excessive brightness can besuppressed, and the power consumption can be reduced. The second mode issuitable for displaying a clear (still and moving) image or the like.Note that the second mode may be referred to as an emissive display mode(emission mode) because display is performed using light emission, i.e.emitted light.

[Third Mode]

In the third mode, display is performed utilizing both light reflectedfrom the first display element and light emitted from the second displayelement. The display in which the first display element and the seconddisplay element are combined can be performed by driving the firstdisplay element and the second display element independently of eachother in the same period. In this specification and the like, thedisplay in which the first display element and the second displayelement are combined, i.e. the third mode, can be referred to as ahybrid display mode (HB display mode). Alternatively, the third mode maybe referred to as a display mode in which an emissive display mode and areflective display mode are combined (ER-hybrid mode).

The display in the third mode can be clearer than that in the first modeand can have lower power consumption than that in the second mode. Forexample, the third mode is effective when the illuminance is relativelylow, e.g., under indoor illumination or in the morning or evening, orwhen the external light does not represent a white chromaticity.Furthermore, the use of mixed light of reflected light and emitted lightenables an image like a painting to be displayed.

According to another embodiment of the present invention, for example, asubtitle can be displayed by the first display element, and an image canbe displayed by the second display element. In order to display both theimage and the subtitle, the display device is driven in theabove-described third mode.

In the case where subtitles are not displayed, an image may be displayedby the second display element; thus, the display device may be driven inthe above-described second mode. In the case where the illuminance ishigh, an image may be displayed by the first display element; thus, thedisplay device may be driven not in the second mode but in the firstmode.

<Specific Example of First to Third Modes>

Here, a specific example of the case where the above-described first tothird modes are employed will be described with reference to FIGS. 13Ato 13D and FIGS. 14A to 14D.

Note that the case where the first to third modes are switchedautomatically in accordance with the illuminance will be describedbelow. In this case, for example, the display mode can be switched inaccordance with data from an illuminance sensor or the like provided inthe display device.

FIGS. 13A to 13C are schematic diagrams of a pixel for describingpossible display modes of the display device of this embodiment.

FIGS. 13A to 13C illustrate a first display element 201, a seconddisplay element 202, an opening 203, reflected light 204 that isreflected from the first display element 201, and transmitted light 205emitted from the second display element 202 through the opening 203.Note that FIG. 13A, FIG. 13B, and FIG. 13C are diagrams illustrating afirst mode, a second mode, and a third mode, respectively.

FIGS. 13A to 13C illustrate the case where a reflective liquid crystalelement is used as the first display element 201 and a self-luminousOLED is used as the second display element 202.

In the first mode illustrated in FIG. 13A, grayscale can be expressed byadjusting the intensity of reflected light with the use of thereflective liquid crystal element, i.e. the first display element 201.For example, as illustrated in FIG. 13A, the intensity of the reflectedlight 204 reflected from the reflective electrode of the reflectiveliquid crystal element, i.e. the first display element 201, is adjustedwith the liquid crystal layer. In this manner, grayscale can beexpressed.

In the second mode illustrated in FIG. 13B, grayscale can be expressedby adjusting the emission intensity of the self-luminous OLED, i.e. thesecond display element 202. Note that light emitted from the seconddisplay element 202 passes through the opening 203 and is extracted tothe outside as the transmitted light 205.

The third mode illustrated in FIG. 13C is a display mode in which thefirst mode and the second mode described above are combined. Forexample, as illustrated in FIG. 13C, grayscale is expressed by adjustingthe intensity of the reflected light 204 reflected from the reflectiveelectrode of the reflective liquid crystal element, i.e. the firstdisplay element 201, with the liquid crystal layer. In a period in whichthe first display element 201 is driven, grayscale is expressed byadjusting the emission intensity of the self-luminous OLED, i.e. thesecond display element 202, namely the intensity of the transmittedlight 205.

<State Transition of First to Third Modes>

Next, the state transition of the first to third modes will be describedwith reference to FIG. 13D. FIG. 13D is a state transition diagram ofthe first mode, the second mode, and the third mode. In FIG. 13D, astate C1, a state C2, and a state C3 correspond to the first mode, thesecond mode, and the third mode, respectively.

As illustrated in FIG. 13D, the display mode can be selected from thestates C1 to C3 in accordance with the illuminance. For example, underhigh illuminance such as in the day time, the state C1 can be selected.In the case where the illuminance decreases as time passes from day tonight, the state C1 transitions to the state C2. Even in the day time,in the case where the illuminance becomes too low to sufficientlyexpress grayscale with reflected light, the state C1 transitions to thestate C3. Needless to say, transition from the state C3 to the state C1,transition from the state C2 to the state C3, transition from the stateC3 to the state C2, or transition from the state C2 to the state C1 alsooccurs.

Note that FIG. 13D illustrates the sun, the moon, and a cloud as imagesrepresenting the first mode, the second mode, and the third mode,respectively.

As illustrated in FIG. 13D, in the case where the illuminance does notchange or slightly changes in the states C1 to C3, the present state maybe maintained without transitioning to another state.

The above configuration in which the display mode is switched inaccordance with the illuminance enables a reduction in the frequency atwhich grayscale is expressed by the intensity of light of thelight-emitting element, which requires a relatively high powerconsumption. Accordingly, the power consumption of the display devicecan be reduced. Furthermore, the operation mode of the display devicecan be switched in accordance with the amount of remaining batterypower, the display contents, or the ambient illuminance. Although thecase where the display mode is automatically switched in accordance withthe illuminance is described above as an example, one embodiment of thepresent invention is not limited thereto, and a user may switch thedisplay mode manually.

<Operation Mode>

Next, operation modes which can be performed by the first displayelement and the second display element will be described with referenceto FIGS. 14A to 14D.

A normal driving mode (normal mode) with a normal frame frequency(typically, higher than or equal to 60 Hz and lower than or equal to 240Hz) and an IDS driving mode with a low frame frequency will be describedbelow as examples.

Note that the IDS driving mode refers to a driving method in which afterimage data is written, rewriting of the image data is stopped. Thisincreases the interval between writing of image data and subsequentwriting of image data, thereby reducing the power that would be consumedby writing of image data in that interval. The IDS driving mode can beperformed at a frame frequency which is 1/100 to 1/10 of that in thenormal driving mode, for example.

FIGS. 14A to 14C are a circuit diagram and timing charts whichillustrate the normal driving mode and the IDS driving mode. Note thatFIG. 14A illustrates the first display element 201 (here, a liquidcrystal element) and a pixel circuit 206 electrically connected to thefirst display element 201. In the pixel circuit 206 in FIG. 14A, asignal line SL, a gate line GL, a transistor M1 connected to the signalline SL and the gate line GL, and a capacitor C_(SLC) connected to thetransistor M1 are illustrated.

A transistor including a metal oxide in a semiconductor layer ispreferably used as the transistor M1. As a typical example of thetransistor, a transistor including an oxide semiconductor which is akind of metal oxide (OS transistor) will be described. The OS transistorhas an extremely low leakage current in a non-conduction state(off-state current); therefore, by turning off the OS transistor, chargecan be retained in a pixel electrode of the liquid crystal element.

FIG. 14B is a timing chart showing the waveforms of signals supplied tothe signal line SL and the gate line GL in the normal driving mode. Inthe normal driving mode, a normal frame frequency (e.g., 60 Hz) is usedfor operation. Here, periods T₁ to T₃ each denote one frame period; ineach frame period, a scanning signal is supplied to the gate line GL,and data D₁ is written from the signal line SL. This operation isperformed both to write the same data D₁ in the periods T₁ to T₃ and towrite different data in the periods T₁ to T₃.

FIG. 14C is a timing chart showing the waveforms of signals supplied tothe signal line SL and the gate line GL in the IDS driving mode. In theIDS driving, a low frame frequency (e.g., 1 Hz) is used for operation.One frame period is denoted by a period T₁ and includes a data writingperiod T_(W) and a data retention period T_(RET). In the IDS drivingmode, a scanning signal is supplied to the gate line GL and the data D₁of the signal line SL is written in the period T_(W), and the gate lineGL is fixed to a low-level voltage in the period T_(RET) to turn off thetransistor M1 and retain the written data D₁.

Note that IDS driving of the second display element can also beperformed in some cases.

The IDS driving of the second display element will be described. FIG.14D illustrates the second display element 202 (here, an organic ELelement) and a pixel circuit 207 electrically connected to the seconddisplay element. In the pixel circuit 207 illustrated in FIG. 14D, asignal line DL, a gate line GL2, a current supply line AL, a transistorM2 electrically connected to the signal line DL and the gate line GL2, acapacitor C_(SEL) electrically connected to the transistor M2 and thecurrent supply line AL, and a transistor M3 electrically connected tothe transistor M2, the capacitor C_(SEL), the current supply line AL,and the second display element 202 are illustrated.

The transistor M2 is preferably an OS transistor like the transistor M1.The OS transistor has an extremely low leakage current in anon-conduction state (off-state current); therefore, charge accumulatedin the capacitor C_(SEL) can be retained by turning off the OStransistor. In other words, the gate-drain voltage of the transistor M3can be kept constant, whereby the emission intensity of the seconddisplay element 202 can be constant.

Therefore, as in the IDS driving of the first display element, the IDSdriving of the second display element is performed as follows: ascanning signal is supplied to the gate line GL2, data is written fromthe signal line DL, and then, the gate line GL2 is fixed to a low-levelvoltage to turn off the transistor M2 and retain the written data.

The transistor M3 is preferably formed using a material similar to thatof the transistor M2. The use of the same material for the transistor M3and the transistor M2 can shorten the fabrication process of the pixelcircuit 207.

The combination of the IDS driving mode with the aforementioned first tothird modes can enhance the effect of reducing the power consumption.

As described above, the display device of this embodiment can performdisplay by switching between the first to third modes. Thus, anall-weather display device or a highly convenient display device havinghigh visibility regardless of the ambient brightness can be obtained.

The display device of this embodiment preferably includes a plurality offirst pixels including first display elements and a plurality of secondpixels including second display elements. The first pixels and thesecond pixels are each preferably arranged in a matrix.

Each of the first pixels and the second pixels can include one or moresub-pixels. The pixel can include, for example, one sub-pixel (e.g., awhite (W) sub-pixel), three sub-pixels (e.g., red (R), green (G), andblue (B) sub-pixels), or four sub-pixels (e.g., red (R), green (G), blue(B), and white (W) sub-pixels, or red (R), green (G), blue (B), andyellow (Y) sub-pixels). Note that color elements included in the firstand second pixels are not limited to the above examples and may becombined with cyan (C), magenta (M), or the like as necessary.

The display device of this embodiment can be configured to display afull color image with the use of either the first pixels or the secondpixels. Alternatively, the display device of this embodiment can beconfigured to display a black-and-white image or a grayscale image withthe use of the first pixels and display a full-color image with the useof the second pixels. The first pixels, which can be used for displayinga black-and-white image or a grayscale image, are suitable fordisplaying information that need not be displayed in color, such as textinformation.

<Schematic Perspective View of Display Device>

Next, a display device of this embodiment will be described withreference to FIG. 15. FIG. 15 is a schematic perspective view of adisplay device 210.

In the display device 210, a substrate 2570 and a substrate 2770 areattached to each other. In FIG. 15, the substrate 2770 is denoted by adashed line.

The display device 210 includes a display portion 214, a circuit 216, awiring 218, and the like. FIG. 15 illustrates an example in which thedisplay device 210 is provided with an IC 220 and an FPC 222. Thus, thestructure illustrated in FIG. 15 can be regarded as a display moduleincluding the display device 210, the IC 220, and the FPC 222.

As the circuit 216, for example, a scan line driver circuit can be used.

The wiring 218 has a function of supplying signals and power to thedisplay portion 214 and the circuit 216. The signals and the power areinput to the wiring 218 from the outside through the FPC 222 or from theIC 220.

FIG. 15 illustrates an example in which the IC 220 is provided over thesubstrate 2570 by a chip on glass (COG) method or the like. An ICincluding a scan line driver circuit, a signal line driver circuit, orthe like can be used as the IC 220, for example. Note that the displaydevice 210 is not necessarily provided with the IC 220. The IC 220 maybe mounted on the FPC by a chip on film (COF) method or the like.

FIG. 15 also shows an enlarged view of part of the display portion 214.In the display portion 214, electrodes 2751 of a plurality of displayelements are arranged in a matrix. Each of the electrodes 2751 has afunction of reflecting visible light and serves as a reflectiveelectrode of a liquid crystal element, i.e. a first display element 2750(described later).

Furthermore, as illustrated in FIG. 15, the electrode 2751 includes aregion 2751H as an opening. In addition, as a light-emitting element,the display portion 214 includes a second display element 2550 that ispositioned closer to the substrate 2570 than the electrode 2751. Lightfrom the second display element 2550 is emitted to the substrate 2770side through the region 2751H of the electrode 2751. The area of alight-emitting region of the second display element 2550 may be equal tothe area of the region 2751H. One of the area of the light-emittingregion of the second display element 2550 and the area of the region2751H is preferably larger than the other because a margin formisalignment can be increased.

<Cross-Sectional View of Input/Output Panel>

Next, a structure of an input/output panel in which a touch sensor isprovided in the display device 210 illustrated in FIG. 15 will bedescribed with reference to FIG. 16, FIGS. 17A to 17D, FIG. 18, and FIG.19. Note that the input/output panel described below is a touch sensordisplay portion with a full-in-cell structure in which a commonelectrode of a reflective liquid crystal element serving as a firstdisplay element is also used as a touch sensor electrode. In addition,as the touch sensor, a projected capacitive (mutual capacitive) touchsensor is used.

FIG. 16 is a cross-sectional view of a pixel included in an input/outputpanel 2700TP3.

FIGS. 17A to 17D illustrate the structure of the input/output panel ofone embodiment of the present invention. FIG. 17A is a cross-sectionalview of an antireflection film (e.g., an antiglare film or a film inwhich an antireflection film is combined with an antiglare film)illustrated in FIG. 16. FIG. 17B is a cross-sectional view illustratingthe structure of a functional film in the input/output panel. FIG. 17Cis a cross-sectional view illustrating the structure of a second unit.FIG. 17D is a cross-sectional view illustrating the structure of a firstunit.

FIG. 18 is an enlarged cross-sectional view of a transistor M includedin the input/output panel 2700TP3 in FIG. 16.

FIG. 19 is a cross-sectional view of the input/output panel 2700TP3 inFIG. 16 and illustrates the operation of a touch sensor portion includedin the input/output panel 2700TP3.

The input/output panel 2700TP3 shown in this structure example includesa pixel 2702(i,j) (see FIG. 16). The input/output panel 2700TP3 includesa first unit 2010, a second unit 2020, and a functional film 2770P (seeFIGS. 17A to 17D). The first unit 2010 includes a functional layer 2520,and the second unit 2020 includes a functional layer 2720.

«Pixel 2702(i,j)»

The pixel 2702(i,j) includes part of the functional layer 2520, a firstdisplay element 2750(i,j), and a second display element 2550(i,j) (seeFIG. 16).

The functional layer 2520 includes a first conductive film, a secondconductive film, an insulating film 2501C, an insulating film 2413, anda pixel circuit (see FIG. 18). The pixel circuit includes the transistorM, for example. The functional layer 2520 includes an optical element2560, a covering film 2565, an insulating film 2412, and a lens 2580.The functional layer 2520 includes part of an insulating film 2521. Astack of an insulating film 2521A and an insulating film 2521B can beused as the insulating film 2521.

For example, a material with a refractive index of approximately 1.55can be used for the insulating film 2521A or the insulating film 2521B.Alternatively, a material with a refractive index of approximately 1.6can be used for the insulating film 2521A or the insulating film 2521B.Alternatively, an acrylic resin or polyimide can be used for theinsulating film 2521A or the insulating film 2521B.

The insulating film 2501C includes a region positioned between the firstconductive film and the second conductive film and has an opening 2591A.

The first conductive film is electrically connected to the first displayelement 2750(i,j). Specifically, the first conductive film iselectrically connected to an electrode 2751(i,j) of the first displayelement 2750(i,j). The electrode 2751(i,j) can be used as the firstconductive film.

The second conductive film includes a region overlapping with the firstconductive film. The second conductive film is electrically connected tothe first conductive film in the opening 2591A. For example, theconductive film 2512B can be used as the second conductive film. Thesecond conductive film is electrically connected to the pixel circuit.For example, a conductive film which functions as a source electrode ora drain electrode of a transistor used as a switch SW1 of the pixelcircuit can be used as the second conductive film. Note that the firstconductive film which is electrically connected to the second conductivefilm in the opening 2591A provided in the insulating film 2501C can bereferred to as a through electrode.

The insulating film 2413 includes a region positioned between the pixelcircuit and the insulating film 2521A and has an opening in a connectionportion 2522.

It is preferable that the insulating film 2413 transmit light and have afunction of preventing entry of an impurity which affects the pixelcircuit, such as water or hydrogen. For the insulating film 2413, forexample, silicon nitride or silicon nitride oxide is preferably used.

The insulating film 2412 includes a region positioned between theinsulating film 2521A and the insulating film 2521B and has an openingin the connection portion 2522.

It is preferable that the insulating film 2412, which is positionedbetween the insulating film 2521A and the insulating film 2521B,transmit light and have a function of preventing entry of an impuritywhich affects the pixel circuit, such as water or hydrogen. For theinsulating film 2412, for example, silicon nitride or silicon nitrideoxide is preferably used.

A conductive film 2566 can be formed using the same material as thecovering film 2565 described later.

The second display element 2550(i,j) is electrically connected to thepixel circuit. The second display element 2550(i,j) has a function ofemitting light toward the functional layer 2520. For example, the seconddisplay element 2550(i,j) has a function of emitting light toward thelens 2580 or the optical element 2560.

The second display element 2550(i,j) is provided so that the displayusing the second display element 2550(i,j) can be perceived from part ofa region from which the display using the first display element2750(i,j) can be perceived. For example, the electrode 2751(i,j) of thefirst display element 2750(i,j) includes the region 2751H in which lightemitted from the second display element 2550(i,j) is not blocked. Notethat dashed arrows in FIG. 16 denote the directions in which externallight is incident on and reflected from the first display element2750(i,j) that displays image data by controlling the intensity ofexternal light reflection. In addition, a solid arrow in FIG. 16 denotesthe direction in which the second display element 2550(i,j) emits lightto the part of the region from which the display using the first displayelement 2750(i,j) can be perceived.

Accordingly, the display using the second display element can beperceived from the part of the region from which the display using thefirst display element can be perceived. Alternatively, a user canperceive the display without changing the orientation or the like of theinput/output panel. Alternatively, an object color expressed by lightreflected from the first display element and a light source colorexpressed by light emitted from the second display element can becombined. Alternatively, an object color and a light source color can beused to display an image like a painting. Thus, a novel input/outputpanel that is highly convenient or reliable can be provided.

For example, the first display element 2750(i,j) includes the electrode2751(i,j), an electrode 2752(i,j), and layer 2753 containing a liquidcrystal material. Note that the first display element 2750(i,j) includesan insulating film 2414, although its reference numeral is not writtenin the closing curly bracket denoting the first display element2750(i,j). Specifically, a reflective liquid crystal element can be usedas the first display element 2750(i,j).

The electrode 2752(i,j) is provided so that an electric field whichextends in the direction intersecting the thickness direction of thelayer 2753 containing a liquid crystal material is formed between theelectrode 2751(i,j) and the electrode 2752(i,j). For example, theelectrode 2752(i,j) can have a comb-like shape, in which case anelectric field which extends in the direction intersecting the thicknessdirection of the layer 2753 containing a liquid crystal material can beformed between the electrode 2751(i,j) and the electrode 2752(i,j).Alternatively, as the first display element, a display element whichoperates in a vertical alignment in-plane-switching (VA-IPS) mode can beused, for example.

For example, a transparent conductive film with a refractive index ofapproximately 2.0 can be used for the electrode 2752(i,j) or theelectrode 2751(i,j). Specifically, an oxide containing indium, tin, andsilicon can be used for the electrode 2752(i,j) or the electrode2751(i,j). Alternatively, a material with a refractive index ofapproximately 1.6 can be used for an alignment film. The dielectricanisotropy of the liquid crystal layer is preferably greater than orequal to 2 and less than or equal to 3.8, and the resistivity of theliquid crystal layer is preferably higher than or equal to 1.0×10¹⁴ Ω·cmand lower than or equal to 1.0×10¹⁵ Ω·cm. In this case, the IDS drivingcan be performed, and the power consumption of the input/output panelcan be reduced.

The insulating film 2414 includes a region positioned between theelectrode 2751(i,j) and the electrode 2752(i,j). It is preferable thatthe insulating film 2414 transmit light and have a function ofpreventing entry of an impurity which affects the pixel circuit, such aswater or hydrogen. For the insulating film 2414, for example, siliconnitride or silicon nitride oxide is preferably used.

For example, the second display element 2550(i,j) includes an electrode2551(i,j), an electrode 2552, and a layer 2553(j) containing alight-emitting material. Note that the second display element 2550(i,j)includes an insulating film 2411, although its reference numeral is notwritten in the opening curly bracket denoting the second display element2550(i,j). The electrode 2552 includes a region overlapping with theelectrode 2551(i,j). The layer 2553(j) containing a light-emittingmaterial includes a region positioned between the electrode 2551(i,j)and the electrode 2552. The electrode 2551(i,j) is electricallyconnected to the pixel circuit in the connection portion 2522.Specifically, an organic EL element can be used as the second displayelement 2550(i,j).

For example, a transparent conductive film with a refractive index ofapproximately 2.0 can be used for the electrode 2551(i,j). Specifically,an oxide containing indium, tin, and silicon can be used for theelectrode 2551(i,j). Alternatively, a material with a refractive indexof approximately 1.8 can be used for the layer 2553(j) containing alight-emitting material.

It is preferable that the insulating film 2411 transmit light and have afunction of preventing entry of an impurity which affects the pixelcircuit, such as water or hydrogen. For the insulating film 2411, forexample, silicon nitride, silicon nitride oxide, or aluminum oxide ispreferably used, and further preferably, a stacked film of any of thesematerials is used.

The optical element 2560 transmits light and includes a first region, asecond region, and a third region.

The first region includes a region to which visible light is suppliedfrom the second display element 2550(i,j), the second region includes aregion in contact with the covering film 2565, and the third region hasa function of emitting part of visible light. The third region has anarea which is smaller than or equal to the area of the region of thefirst region to which visible light is supplied.

The covering film 2565 reflects visible light and has a function ofreflecting part of visible light and supplying it to the third region.

For example, a metal can be used for the covering film 2565.Specifically, a material containing silver can be used for the coveringfilm 2565. For example, a material containing silver, palladium, and thelike or a material containing silver, copper, and the like can be usedfor the covering film 2565.

Note that a region between the first display element 2750(i,j) and thesecond display element 2550(i,j) has a thickness of less than 30 μm,preferably less than 10 μm, further preferably less than 5 μm.

«Transistor M»

The transistor M has a dual-gate structure including a first gateelectrode and a second gate electrode (see FIG. 18).

The transistor M includes the insulating film 2521A, the insulating film2413, a conductive film 2511 a, a conductive film 2511 b, an insulatingfilm 2402, an insulating film 2403, a conductive film 2514, aninsulating film 2404, a semiconductor film 2531, an insulating film2405, a conductive film 2513, and the insulating film 2501C.

The insulating film 2521A, the insulating film 2413, and the insulatingfilm 2501C are described in other parts of this specification;therefore, description of these films are omitted here.

The conductive film 2511 a functions as one of a source electrode and adrain electrode of the transistor M, and the conductive film 2511 bfunctions as the other of the source electrode and the drain electrode.

A metal such as aluminum, titanium, chromium, nickel, copper, yttrium,zirconium, molybdenum, silver, tantalum, or tungsten, or an alloycontaining the metal as its main component can be used for the conductorfilm 2511 a and the conductive film 2511 b. In particular, a metalnitride film such as a tantalum nitride film is preferable because ithas a barrier property against hydrogen or oxygen and has a highoxidation resistance.

The conductive film 2511 a and the conductive film 2511 b can be formedusing the same material as the conductive film 2512B or the secondconductive film, for example.

Although the drawing illustrates a single-layer structure, theconductive film 2511 a and the conductive film 2511 b may each have astacked structure of two or more layers. For example, a tantalum nitridefilm and a tungsten film may be stacked. Alternatively, a titanium filmand an aluminum film may be stacked. Other examples include a two-layerstructure in which an aluminum film is stacked over a tungsten film, atwo-layer structure in which a copper film is stacked over acopper-magnesium-aluminum alloy film, a two-layer structure in which acopper film is stacked over a titanium film, and a two-layer structurein which a copper film is stacked over a tungsten film.

The conductive film 2514 functions as a first gate electrode (simplyreferred to as a gate electrode in some cases) of the transistor M, andthe conductive film 2513 functions as a second gate electrode (referredto as a back gate electrode in some cases) of the transistor M.

The conductive film 2514 can be formed using, for example, a metalselected from aluminum, chromium, copper, tantalum, titanium,molybdenum, and tungsten, an alloy containing the metal as a component,or an alloy containing any of these metals in combination. Inparticular, a metal nitride film such as a tantalum nitride film ispreferable because it has a barrier property against hydrogen or oxygenand has a high oxidation resistance. Furthermore, manganese and/orzirconium may be used. Alternatively, a semiconductor typified bypolycrystalline silicon doped with an impurity element such asphosphorus, or a silicide such as nickel silicide may be used. Althoughthe drawing illustrates a single-layer structure, a stacked structure oftwo or more layers may be employed.

For example, a two-layer structure in which a titanium film is stackedover an aluminum film is preferably employed. Other examples include atwo-layer structure in which a titanium film is stacked over a titaniumnitride film, a two-layer structure in which a tungsten film is stackedover a titanium nitride film, and a two-layer structure in which atungsten film is stacked over a tantalum nitride film or a tungstennitride film.

Another example is a three-layer structure in which a titanium film, analuminum film, and a titanium film are stacked in this order.Alternatively, an alloy film or a nitride film which contains aluminumand one or more metals selected from titanium, tantalum, tungsten,molybdenum, chromium, neodymium, and scandium may be used.

The conductive film 2514 can also be formed using a light-transmittingconductive material such as indium tin oxide, indium oxide containingtungsten oxide, indium zinc oxide containing tungsten oxide, indiumoxide containing titanium oxide, indium tin oxide containing titaniumoxide, indium zinc oxide, or indium tin oxide to which silicon oxide isadded. The conductive film 2514 can have a stacked structure containingany of the above light-transmitting conductive materials and any of theabove metals.

As the conductive film 2513, for example, a metal film containing anelement selected from molybdenum, titanium, tantalum, tungsten,aluminum, copper, chromium, neodymium, and scandium or a metal nitridefilm containing the element as a component (e.g., a tantalum nitridefilm, a titanium nitride film, a molybdenum nitride film, or a tungstennitride film) can be used. In particular, a metal nitride film such as atantalum nitride film is preferable because it has a barrier propertyagainst hydrogen or oxygen and is difficult to oxidize (has a highoxidation resistance). It is also possible to use a conductive materialsuch as indium tin oxide, indium oxide containing tungsten oxide, indiumzinc oxide containing tungsten oxide, indium oxide containing titaniumoxide, indium tin oxide containing titanium oxide, indium zinc oxide, orindium tin oxide to which silicon oxide is added. Although the drawingillustrates a single-layer structure, a stacked structure of two or morelayers may be employed.

Furthermore, the conductive film 2513 may be formed using the samematerial as a conductive film which electrically connects the firstconductive film to the second conductive film in the opening 2591A.

The semiconductor film 2531 includes a region in which a channel of thetransistor M is formed. A metal oxide described in Embodiment 6,particularly a CAC-OS, is preferably used for the semiconductor film2531.

In the case where the semiconductor film 2531 includes a metal oxide, aninsulating film containing oxygen, such as a silicon oxide film or asilicon oxynitride film, is preferably used as each of the insulatingfilms 2402 to 2405. In particular, the insulating film 2403 ispreferably formed using an insulator containing excess oxygen(containing oxygen in excess of that in the stoichiometric composition).When such an insulator containing excess oxygen is provided in contactwith the semiconductor film 2531 which includes a metal oxide, oxygenvacancies in the semiconductor film 2531 can be compensated. Note thatthe insulating films 2402 to 2405 are not necessarily formed using thesame material.

The insulating film 2404 can have a single-layer structure or a stackedstructure using an insulator containing silicon oxide, siliconoxynitride, silicon nitride oxide, aluminum oxide, hafnium oxide,tantalum oxide, zirconium oxide, lead zirconate titanate (PZT),strontium titanate (SrTiO₃), (Ba,Sr)TiO₃ (BST), or the like.Alternatively, aluminum oxide, bismuth oxide, germanium oxide, niobiumoxide, silicon oxide, titanium oxide, tungsten oxide, yttrium oxide, orzirconium oxide may be added to the insulator, for example.Alternatively, the insulator may be subjected to nitriding treatment.Silicon oxide, silicon oxynitride, or silicon nitride may be stackedover the above insulator.

As in the case of the insulating film 2403, an oxide insulator whichcontains more oxygen than the stoichiometric composition is preferablyused for the insulating film 2404. When such an insulator containingexcess oxygen is provided in contact with the semiconductor film 2531which includes a metal oxide, oxygen vacancies in the semiconductor film2531 can be reduced.

As the insulating film 2404, an insulating film which is formed ofaluminum oxide, aluminum oxynitride, gallium oxide, gallium oxynitride,yttrium oxide, yttrium oxynitride, hafnium oxide, hafnium oxynitride,silicon nitride, or the like and has a barrier property against oxygenor hydrogen can be used. The insulating film 2404 formed of such amaterial functions as a layer that prevents release of oxygen from thesemiconductor film 2531 which includes a metal oxide and entry of animpurity such as hydrogen from the outside.

Note that the insulating film 2404 may have a structure similar to thatof the insulating film 2402, the insulating film 2403, or the insulatingfilm 2405. Although the drawing illustrates a single-layer structure,the insulating films 2402 to 2405 may each have a stacked structure oftwo or more layers.

Note that the structure of the input/output panel 2700TP3 is not limitedto the structure example illustrated in FIG. 16, FIGS. 17A to 17D, FIG.18, and FIG. 19, in which the channel formation region of the transistorM includes a metal oxide. For example, a transistor whose channelformation region includes silicon may be used as the transistor M.

«Lens 2580»

A material that transmits visible light can be used for the lens 2580.

Alternatively, a material with a refractive index of greater than orequal to 1.3 and less than or equal to 2.5 can be used for the lens2580. For example, an inorganic material or an organic material can beused for the lens 2580.

For example, a material containing an oxide or a sulfide can be used forthe lens 2580.

Specifically, cerium oxide, hafnium oxide, lanthanum oxide, magnesiumoxide, niobium oxide, tantalum oxide, titanium oxide, yttrium oxide,zinc oxide, an oxide containing indium and tin, an oxide containingindium, gallium, and zinc, or the like can be used for the lens 2580.Alternatively, zinc sulfide or the like can be used for the lens 2580.

For example, a material containing a resin can be used for the lens2580. Specifically, a resin into which chlorine, bromine, or iodine isintroduced, a resin into which heavy metal atoms are introduced, a resininto which an aromatic ring is introduced, a resin into which sulfur isintroduced, or the like can be used for the lens 2580. Alternatively, astack of a resin and a resin having a higher refractive index than theresin can be used for the lens 2580. The resin having a higherrefractive index may contain nanoparticles. Titanium oxide, zirconiumoxide, or the like can be used for the nanoparticles.

«Functional layer 2720»

The functional layer 2720 includes a region positioned between thesubstrate 2770 and an insulating film 2415. The functional layer 2720includes an insulating film 2771 and a coloring film CF1.

The coloring film CF1 includes a region positioned between the substrate2770 and the first display element 2750(i,j).

The insulating film 2771 includes a region positioned between thecoloring film CF1 and the layer 2753 containing a liquid crystalmaterial. The insulating film 2771 can reduce unevenness due to thethickness of the coloring film CF1. Furthermore, the insulating film2771 can prevent impurities from diffusing from the coloring film CF1 orthe like into the layer 2753 containing a liquid crystal material.

For example, an acrylic resin with a refractive index of approximately1.55 can be used for the insulating film 2771.

The insulating film 2415 includes a region positioned between theinsulating film 2771 and the layer 2753 containing a liquid crystalmaterial.

It is preferable that the insulating film 2415 transmit light and have afunction of preventing entry of an impurity which affects the pixelcircuit, such as water or hydrogen. For the insulating film 2415, forexample, silicon nitride or silicon nitride oxide is preferably used.

«Substrate 2570, substrate 2770, and substrate 2870»

The input/output panel described in this embodiment includes thesubstrate 2570, the substrate 2770, and a substrate 2870.

The substrate 2770 includes a region overlapping with the substrate 2570and the substrate 2870. The substrate 2770 includes a region in whichthe functional layer 2520 is positioned between the substrate 2770 andthe substrate 2570.

The substrate 2770 includes a region overlapping with the first displayelement 2750(i,j). For example, a material with low birefringence can beused for the region.

For example, a resin material with a refractive index of approximately1.5 can be used for the substrate 2770.

The substrate 2870 includes a region in which functional films 2770P and2770D are positioned between the substrate 2770 and the substrate 2870.

The substrate 2870 includes a region overlapping with the first displayelement 2750(i,j). For example, a material with low birefringence can beused for the region.

Note that the substrate 2870 is not necessarily provided in theinput/output panel 2700TP3.

«Bonding Layer 2505»

The input/output panel described in this embodiment also includes abonding layer 2505.

The bonding layer 2505 includes a region positioned between thefunctional layer 2520 and the substrate 2570 and has a function ofbonding the functional layer 2520 and the substrate 2570 together.

«Structure Body KB1 and Structure Body KB2»

The input/output panel described in this embodiment also includes astructure body KB1 and a structure body KB2.

The structure body KB1 has a function of providing a certain spacebetween the functional layer 2520 and the substrate 2770. The structurebody KB1 includes a region overlapping with the region 2751H and has alight-transmitting property. Thus, light emitted from the second displayelement 2550(i,j) can be supplied to one surface of the structure bodyKB1 and extracted through the other surface of the structure body KB1.

Furthermore, the structure body KB1 includes a region overlapping withthe optical element 2560 and is formed using a material whose refractiveindex is different from that of a material used for the optical element2560 by 0.2 or less, for example. Thus, light emitted from the seconddisplay element can be efficiently utilized. The area of the seconddisplay element can be increased. The density of a current flowing tothe organic EL element can be reduced.

The structure body KB2 has a function of controlling the thickness of apolarizing layer 2770PB to a predetermined thickness. The structure bodyKB2 includes a region overlapping with the second display element2550(i,j) and has a light-transmitting property.

Alternatively, a material that transmits light of a predetermined colorcan be used for the structure body KB1 or the structure body KB2. Thus,the structure body KB1 or the structure body KB2 can be used as a colorfilter, for example. For example, a material that transmits blue, green,or red light can be used for the structure body KB1 or the structurebody KB2. A material that transmits yellow light, white like, or thelike can be used for the structure body KB1 or the structure body KB2.

Specifically, polyester, polyolefin, polyamide, polyimide,polycarbonate, polysiloxane, an acrylic resin, or the like, a compositematerial of a plurality of resins selected from these resins, or thelike can be used for the structure body KB1 or the structure body KB2.Alternatively, a photosensitive material may be used.

For example, an acrylic resin with a refractive index of approximately1.5 can be used for the structure body KB1. In addition, an acrylicresin with a refractive index of approximately 1.55 can be used for thestructure body KB2.

«Functional Film 2770D, Functional Film 2770P, Functional Film 2770AG,and the Like»

The input/output panel 2700TP3 described in this embodiment includes thefunctional film 2770D, the functional film 2770P, and a functional film2770AG.

The functional film 2770D includes a region overlapping with the firstdisplay element 2750(i,j). The functional film 2770D includes a regionin which the first display element 2750(i,j) is positioned between thefunctional film 2770D and the functional layer 2520.

For example, a light diffusion film can be used as the functional film2770D. Specifically, a material with a columnar structure having an axisalong the direction intersecting a surface of a base can be used for thefunctional film 2770D. In this case, light can be easily transmitted inthe direction along the axis and scattered in other directions. Forexample, light reflected from the first display element 2750(i,j) can bediffused.

A bonding layer 2780 includes a region positioned between the functionalfilm 2770D and the substrate 2770. Thus, the second unit 2020 can beformed.

The functional film 2770P includes the polarizing layer 2770PB, aretardation film 2770PA, and the structure body KB2. The polarizinglayer 2770PB includes an opening, and the retardation film 2770PAincludes a region overlapping with the polarizing layer 2770PB. Notethat the structure body KB2 is provided in the opening.

For example, a dichromatic pigment, a liquid crystal material, and aresin can be used for the polarizing layer 2770PB. The polarizing layer2770PB has a polarization property. In this case, the functional film2770P can be used as a polarizing plate.

The polarizing layer 2770PB includes a region overlapping with the firstdisplay element 2750(i,j), and the structure body KB2 includes a regionoverlapping with the second display element 2550(i,j). Thus, a liquidcrystal element can be used as the first display element. For example, areflective liquid crystal element can be used as the first displayelement. Light emitted from the second display element can be extractedefficiently. The density of a current flowing to the organic EL elementcan be reduced. The reliability of the organic EL element can beincreased.

For example, an antireflection film, a polarizing film, or a retardationfilm can be used for the functional film 2770P. Specifically, a filmcontaining a dichromatic pigment and a retardation film can be used forthe functional film 2770P.

Furthermore, an antistatic film preventing the attachment of a foreignsubstance, a water repellent film suppressing the attachment of stain, ahard coat film suppressing a scratch in use, or the like can be used forthe functional film 2770P.

For example, a material with a refractive index of approximately 1.6 canbe used for the diffusion film. In addition, a material with arefractive index of approximately 1.6 can be used for the retardationfilm 2770PA.

For example, an antireflection film can be used as the functional film2770AG. In the case where an antireflection film is used for thefunctional film 2770P, an antireflection film is not necessarilyprovided as the functional film 2770AG. Examples of the functional film2770AG include an antiglare film and a film serving as both anantireflection film and an antiglare film. The functional film 2770AG isnot necessarily provided in the input/output panel 2700TP3.

«Operation Method of Touch Sensor»

Next, a touch sensor function of the input/output panel 2700TP3 will bedescribed.

As described above, in a full-in-cell touch sensor display portion, asensing operation of a touch sensor is performed using a commonelectrode of a reflective liquid crystal element which is a firstdisplay element as a touch sensor electrode of a touch sensor portion.

A mutual capacitive touch sensor senses a touch by sensing a change inthe capacitance value of a capacitor included in the touch sensor.

Here, a pair of touch sensor electrodes (common electrodes) of thecapacitor corresponds to the electrode 2752(i,j) included in the pixel2702(i,j) and an electrode 2752(i+1,j) included in a pixel 2702(i+1,j)(see FIG. 19).

In FIG. 19, an electric field formed by the electrode 2752(i,j) and theelectrode 2752(i+1,j) is denoted by a thick dashed arrow. Here, theelectrode 2752(i,j) has a higher potential than the electrode2752(i+1,j), and the formed electric field is directed from theelectrode 2752(i,j) to the electrode 2752(i+1,j).

To form such an electric field, a wiring which is electrically connectedto the electrode 2752(i,j) and a wiring which is electrically connectedto the electrode 2752(i+1,j) are preferably provided so as to extend indifferent directions. For example, the wiring which is electricallyconnected to the electrode 2752(i,j) and the wiring which iselectrically connected to the electrode 2752(i+1,j) are preferablyprovided so to as to intersect at right angles. Note that a preferredwiring method will be described in detail in Embodiment 7.

FIG. 19 illustrates a state in which an object 2900 touches theinput/output panel 2700TP3. In FIG. 19, a hand is illustrated as theobject 2900, and a finger touches the input/output panel 2700TP3;however, the object 2900 may be a stylus pen or the like instead of thehand (finger).

Note that this embodiment can be combined with any of the otherembodiments in this specification as appropriate.

Embodiment 5

In this embodiment, a method for operating a hybrid display device whichis different from the method in Embodiment 4 will be described.

Operation Example 1

An electronic device including a hybrid display device and a touchsensor portion will be described. FIG. 20A illustrates a tabletinformation terminal as an example of the electronic device including ahybrid display device and a touch sensor portion.

The electronic device 5200A includes a display portion 5201, a housing5202, and an illuminance sensor 5203. The display portion 5201 includesthe touch sensor portion. Therefore, the display portion 5201 can bereferred to as a touch sensor display portion. The illuminance sensor5203 has a function of measuring the illuminance of external light andis provided for automatic switching between the first to third modesdescribed in Embodiment 4.

The display portion 5201 further includes a reflective liquid crystalelement 21 and a light-transmitting element 22 as components of thehybrid display device. In the case where the display portion 5201includes a capacitive touch sensor portion, a capacitor 23 is provided.

The electronic device 5200A is operated in such a manner that an imagecontent displayed on the display portion 5201 is touched with a finger,a stylus, or the like. For example, FIG. 20A illustrates a state inwhich a hand 5211 of a user operates the electronic device 5200A.

When the user operates the electronic device 5200A, however, a shadow5212 of the hand 5211 of the user may be cast on the display portion5201. In particular, when the electronic device 5200A is used in anenvironment with bright external light, i.e. either in the first mode orthe third mode, the cast shadow 5212 may become darker.

When the shadow 5212 of the hand 5211 of the user is cast on the displayportion 5201, an image displayed on the display portion 5201 isdifficult to see in some cases. In contrast, when the hand 5211 hidesthe shadow 5212 from the user's eyes, the user does not mind the shadow5212 cast on the display portion 5201 in some cases.

Thus, in a preferred configuration of the electronic device 5200A, aportion of an image displayed on the display portion 5201, which is inthe shadow 5212 and is not perceived by the user, is not displayed or isdisplayed with an intentionally reduced quality. In this manner, aportion of an image which is in the shadow 5212 and is not perceived bythe user is not displayed on the display portion 5201, or the luminanceof the portion of the image in the shadow 5212 is reduced; accordingly,the power consumption of the electronic device 5200A can be reduced.

As a method for obtaining such a configuration, an illuminance sensormay be provided in a pixel of the display portion 5201.

Illuminance information for automatic switching between the first tothird modes described in Embodiment 4 is obtained by the illuminancesensor 5203. However, the illuminance of the above-described portion inthe shadow 5212 cast on the display portion 5201 is preferably measuredby an illuminance sensor 24 in each pixel of the display portion 5201.Note that FIG. 20A illustrates a photodiode as the illuminance sensor.Then, the information on the shadow 5212 may be transmitted to aprocessor included in the electronic device 5200A, and the processor maygenerate an image so that a portion of the image in the shadow 5212 isnot displayed or the luminance of the portion of the image in the shadow5212 is reduced.

For example, in the case where the electronic device 5200A is driven inthe first mode according to information on the illuminance measured bythe illuminance sensor 5203, the electronic device 5200A may be drivenin the following manner: in a portion of the display portion 5201, whichis perceived as being in the shadow 5212 by the illuminance sensor 24 ineach pixel, the image is not displayed or the luminance of the image isreduced.

For example, in the case where the electronic device 5200A is driven inthe third mode according to information on the illuminance measured bythe illuminance sensor 5203, the electronic device 5200A may be drivenin the following manner: in a portion of the display portion 5201, whichis perceived as being in the shadow 5212 by the illuminance sensor 24 ineach pixel, the image is not displayed or the operation in the firstmode is performed.

Operation Example 2

Next, an operation method that is different from the above-describedoperation method will be described. For the description of the differentoperation example, an electronic device that is different from theelectronic device 5200A will be used. The electronic device 5200Billustrated in FIG. 20B has substantially the same structure as theelectronic device 5200A, except that the illuminance sensor 24 in thepixel is not provided.

The electronic device 5200B is operated in such a manner that an imagecontent displayed on the display portion 5201 is touched with a finger,a stylus, or the like. For example, FIG. 20B illustrates a state inwhich the hand 5211 of the user operates the electronic device 5200B.

When the user operates the electronic device 5200B, a region 5213 whichis touched by a finger 5211 a of the hand 5211 of the user is formed inthe display portion 5201. Since the region 5213 is hidden by the finger5211 a, an image displayed in the region 5213 is not perceived by theuser.

Thus, in a preferred configuration of the electronic device 5200B, aportion of an image displayed on the display portion 5201, which is inthe region 5213 and is not perceived by the user, is not displayed or isdisplayed with an intentionally reduced quality. In this manner, aportion of an image which is in the region 5213 and is not perceived bythe user is not displayed on the display portion 5201, or the luminanceof the portion of the image in the region 5213 is reduced; accordingly,the power consumption of the electronic device 5200B can be reduced.

Such a configuration can be obtained using the touch sensor portionprovided in the display portion 5201. During the operation of theelectronic device 5200B, a region in which a touch is sensed by thetouch sensor portion may be judged to be the region 5213, theinformation on the region 5213 may be transmitted to a processor or thelike included in the electronic device 5200B, and the processor maygenerate an image so that the portion of the image in the region 5213 isnot displayed or the luminance of the portion of the image in the region5213 is reduced.

For example, in the case where the electronic device 5200B is driven inthe first mode or the second mode according to information on theilluminance measured by the illuminance sensor 5203, the electronicdevice 5200B may be driven in the following manner: in a portion of thedisplay portion 5201, which is perceived as the region 5213 by the touchsensor portion, the image is not displayed or the luminance of the imageis reduced.

For example, in the case where the electronic device 5200B is driven inthe third mode according to information on the illuminance measured bythe illuminance sensor 5203, the electronic device 5200B may be drivenin the following manner: in a portion of the display portion 5201, whichis perceived as the region 5213 by the touch sensor portion, the imageis not displayed or the operation in the first mode is performed.

Note that this embodiment can be combined with any of the otherembodiments in this specification as appropriate.

Embodiment 6

Described in this embodiment is a metal oxide that can be used for atransistor disclosed in this specification. In particular, details abouta metal oxide and a cloud-aligned composite (CAC) will be describedbelow.

A CAC-OS or a CAC metal oxide has a conducting function in a part of thematerial and has an insulating function in another part of the material;as a whole material, the CAC-OS or the CAC metal oxide has asemiconductor function. In the case where the CAC-OS or the CAC metaloxide is used for a channel formation region of a transistor, theconducting function allows electrons (or holes) serving as carriers toflow, and the insulating function prevents electrons serving as carriersfrom flowing. By the complementary effects of the conducting functionand the insulating function, the CAC-OS or the CAC metal oxide can havea switching function (on/off function). In the CAC-OS or the CAC metaloxide, separation of the functions can maximize each function.

The CAC-OS or the CAC metal oxide includes conductive regions andinsulating regions. The conductive regions have the above-describedconducting function, and the insulating regions have the above-describedinsulating function. In some cases, the conductive regions and theinsulating regions in the material are separated at the nanoparticlelevel. In some cases, the conductive regions and the insulating regionsare unevenly distributed in the material. In some cases, conductiveregions which are connected together like clouds and the boundariestherebetween are blurred are observed.

Furthermore, in the CAC-OS or the CAC metal oxide, the conductiveregions and the insulating regions each have a size of greater than orequal to 0.5 nm and less than or equal to 10 nm, preferably greater thanor equal to 0.5 nm and less than or equal to 3 nm and are dispersed inthe material, in some cases.

The CAC-OS or the CAC metal oxide includes components having differentbandgaps. For example, the CAC-OS or the CAC metal oxide includes acomponent having a wide gap due to the insulating region and a componenthaving a narrow gap due to the conductive region. In the case of such acomposition, carriers mainly flow in the component having a narrow gap.The component having a narrow gap complements the component having awide gap, and carriers also flow in the component having a wide gap inconjunction with the component having a narrow gap. Therefore, in thecase where the above-described CAC-OS or the CAC metal oxide is used fora channel formation region of a transistor, the transistor in the onstate can have a high current drive capability, that is, a high on-statecurrent and a high field-effect mobility.

In other words, the CAC-OS or the CAC metal oxide can also be called amatrix composite or a metal matrix composite. Thus, the CAC-OS may alsobe called a cloud-aligned composite OS.

The CAC-OS is, for example, a metal oxide material with a composition inwhich elements are unevenly distributed in regions each having a size ofgreater than or equal to 0.5 nm and less than or equal to 10 nm,preferably greater than or equal to 1 nm and less than or equal to 2 nm,or a similar size. In the following description of a metal oxide, thestate in which one or more metal elements are unevenly distributed inregions each having a size of greater than or equal to 0.5 nm and lessthan or equal to 10 nm, preferably greater than or equal to 1 nm andless than or equal to 2 nm, or a similar size and the regions includingthe metal element(s) are mixed is referred to as a mosaic pattern or apatch-like pattern.

Note that the metal oxide preferably contains at least indium. Inparticular, indium and zinc are preferably contained. In addition, oneor more elements selected from aluminum, gallium, yttrium, copper,vanadium, beryllium, boron, silicon, titanium, iron, nickel, germanium,zirconium, molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum,tungsten, magnesium, and the like may be contained.

As an example of the CAC-OS, an In—Ga—Zn oxide with the CAC composition(such an In—Ga—Zn oxide may be particularly referred to as CAC-IGZO)will be described. The CAC-IGZO has a composition with a mosaic patternin which materials are separated into indium oxide (InO_(X1), where X1is a real number greater than 0) or indium zinc oxide(In_(X2)Zn_(Y2)O_(Z2), where X2, Y2, and Z2 are each a real numbergreater than 0) and gallium oxide (GaO_(X3), where X3 is a real numbergreater than 0) or gallium zinc oxide (Ga_(X4)Zn_(Y4)O_(Z4), where X4,Y4, and Z4 are each a real number greater than 0), for example.Furthermore, InO_(X1) or In_(X2)Zn_(Y2)O_(Z2) forming the mosaic patternis evenly distributed in the film. This composition is also referred toas a cloud-like composition.

That is, the CAC-OS is a composite metal oxide with a composition inwhich a region including GaO_(X3) as a main component and a regionincluding In_(X2)Zn_(Y2)O_(Z2) or InO_(X1) as a main component aremixed. In this specification, for example, when the atomic ratio of Into an element M in a first region is larger than the atomic ratio of Into the element M in a second region, the first region has a higher Inconcentration than the second region.

Note that a compound containing In, Ga, Zn, and O is known as IGZO.Typical examples of IGZO include a crystalline compound represented byInGaO₃(ZnO)_(m1) (m1 is a natural number) and a crystalline compoundrepresented by In_((1+x0))Ga_((1−x0))O₃(ZnO)_(m0) (−1≤x0≤1; m0 is agiven number).

The above crystalline compounds have a single crystal structure, apolycrystalline structure, or a c-axis-aligned crystalline (CAAC)structure. Note that the CAAC structure is a crystal structure in whicha plurality of IGZO nanocrystals has c-axis alignment and is connectedin the a-b plane direction without alignment.

On the other hand, the CAC-OS relates to the material composition of ametal oxide. In part of the material composition of a CAC-OS containingIn, Ga, Zn, and O, nanoparticle regions including Ga as a main componentand nanoparticle regions including In as a main component are observed.These nanoparticle regions are randomly dispersed in a mosaic pattern.Therefore, the crystal structure is a secondary element for the CAC-OS.

Note that the CAC-OS does not include a stacked structure of two or morefilms with different compositions. For example, a two-layer structure ofa film including In as a main component and a film including Ga as amain component is not included.

A boundary between the region including GaO_(X3) as a main component andthe region including In_(X2)Zn_(Y2)O_(Z2) or InO_(X1) as a maincomponent is not clearly observed in some cases.

In part of the composition of a CAC-OS which contains, instead ofgallium, one or more metal elements selected from aluminum, yttrium,copper, vanadium, beryllium, boron, silicon, titanium, iron, nickel,germanium, zirconium, molybdenum, lanthanum, cerium, neodymium, hafnium,tantalum, tungsten, magnesium, and the like, nanoparticle regionsincluding the metal element(s) as a main component(s) and nanoparticleregions including In as a main component are observed. Thesenanoparticle regions are randomly dispersed in a mosaic pattern.

The CAC-OS can be formed by a sputtering method under conditions where asubstrate is not heated intentionally, for example. In the case offorming the CAC-OS by a sputtering method, one or more gases selectedfrom an inert gas (typically, argon), an oxygen gas, and a nitrogen gasmay be used as a deposition gas. The ratio of the flow rate of an oxygengas to the total flow rate of the deposition gas at the time ofdeposition is preferably as low as possible; for example, the flow ratioof an oxygen gas is preferably higher than or equal to 0% and lower than30%, further preferably higher than or equal to 0% and lower than orequal to 10%.

The CAC-OS is characterized in that no clear peak is observed inmeasurement using θ/2θ scan by an out-of-plane method, which is an X-raydiffraction (XRD) measurement method. That is, XRD shows no alignment inthe a-b plane direction and the c-axis direction in a measured region.

In an electron diffraction pattern of the CAC-OS which is obtained byirradiation with an electron beam with a probe diameter of 1 nm (alsoreferred to as a nanometer-sized electron beam), a ring-like region withhigh luminance and a plurality of bright spots in the ring-like regionare observed. Therefore, the electron diffraction pattern indicates thatthe crystal structure of the CAC-OS includes a nanocrystal (nc)structure with no alignment in the plan-view direction and thecross-sectional direction.

For example, an energy dispersive X-ray spectroscopy (EDX) mapping imageconfirms that an In—Ga—Zn oxide with the CAC composition has a structurein which regions including GaO_(X3) as a main component and regionsincluding In_(X2)Zn_(Y2)O_(Z2) or InO_(X1) as a main component areunevenly distributed and mixed.

The CAC-OS has a structure and characteristics different from those ofan IGZO compound in which metal elements are evenly distributed. Thatis, in the CAC-OS, regions including GaO_(X3) or the like as a maincomponent and regions including In_(X2)Zn_(Y2)O_(Z2) or InO_(X1) as amain component are phase-separated from each other in a mosaic pattern.

The conductivity of the region including In_(X2)Zn_(Y2)O_(Z2) orInO_(X1) as a main component is higher than that of the region includingGaO_(X3) or the like as a main component. In other words, when carriersflow through the region including In_(X2)Zn_(Y2)O_(Z2) or InO_(X1) as amain component, the oxide semiconductor exhibits conductivity.Accordingly, when the regions including In_(X2)Zn_(Y2)O_(Z2) or InO_(X1)as a main component are distributed like clouds in the oxidesemiconductor, a high field-effect mobility (μ) can be achieved.

In contrast, the insulating property of the region including GaO_(X3) orthe like as a main component is higher than that of the region includingIn_(X2)Zn_(Y2)O_(Z2) or InO_(X1) as a main component. In other words,when the regions including GaO_(X3) or the like as a main component aredistributed in the oxide semiconductor, leakage current can besuppressed and favorable switching operation can be achieved.

Accordingly, when a CAC-OS is used for a semiconductor element, theinsulating property derived from GaO_(X3) or the like and theconductivity derived from In_(X2)Zn_(Y2)O_(Z2) or InO_(X1) complementeach other, whereby a high on-state current (I_(on)) and a highfield-effect mobility (μ) can be achieved.

A semiconductor element including a CAC-OS has a high reliability. Thus,the CAC-OS is suitably used for a variety of semiconductor devicestypified by a display.

This embodiment can be combined with any of the other embodiments inthis specification as appropriate.

Embodiment 7

In this embodiment, a configuration example of the touch sensor portion(also referred to as a touch sensor, a touch panel, or the like in somecases) mentioned in the above embodiment will be described. Note that inthis embodiment, a projected capacitive (mutual capacitive) touch panelwill be described.

<Block Diagram>

FIG. 21 is a block diagram illustrating a configuration example of atouch panel 400 that is a mutual capacitive touch panel. The touch panel400 includes a sensing region 401. The sensing region 401 includes awiring CL and a wiring ML.

In FIG. 21, for example, six wirings CL(1) to CL(6) represent the wiringCL to which a pulse voltage is applied, and six wirings ML(1) to ML(6)represent the wiring ML which senses a change in current. Note that thenumber of wirings is not limited thereto. FIG. 21 also illustrates acapacitor 404 that is formed of the wiring CL and the wiring ML whichoverlap with each other or are arranged close to each other.

When an object (e.g., a finger or a stylus) approaches or touches thesensing region 401, the capacitance value of the capacitor 404 changes;thus, the touch panel 400 senses a touch.

The touch panel 400 is electrically connected to a touch panel IC 405through the wiring CL and the wiring ML. The touch panel IC 405 includesa driver circuit 402 and a sensing circuit 403.

The driver circuit 402 is electrically connected to the touch panel 400through the wiring CL. The driver circuit 402 has a function ofoutputting a signal Tx. As the driver circuit 402, a shift registercircuit and a buffer circuit can be used in combination, for example.

The sensing circuit 403 is electrically connected to the touch panel 400through the wiring ML. The sensing circuit 403 senses a signal Rx todetermine whether the touch panel 400 has been touched. The sensingcircuit 403 can include an amplifier circuit and an analog-digitalconverter (ADC), for example. The sensing circuit 403 has a function ofconverting an analog signal output from the touch panel 400 to a digitalsignal and outputting the digital signal to an application processor.

<Top View>

Next, a specific configuration example of the touch panel 400 will bedescribed with reference to FIGS. 22A to 22C and FIGS. 23A and 23B.

FIG. 22A is a top view of the touch panel 400. FIGS. 22B and 22C areeach a perspective view illustrating part of FIG. 22A.

FIG. 23A is a top view of a portion in which a control line and asensing signal line are adjacent to each other. FIG. 23B is aperspective view that schematically illustrates an electric fieldgenerated in the adjoining portion.

The touch panel 400 includes the sensing region 401. The sensing region401 includes a wiring CL(g), a wiring ML(h), and a conductive film (seeFIG. 22A). Note that g and h are each an integer of 2 or more.

For example, a conductive film divided into a plurality of regions canbe used for the sensing region 401 (see FIG. 22A). This enables the samepotential or different potentials to be supplied to the plurality ofregions.

Specifically, a conductive film can be divided into a conductive filmthat can be used as the wiring CL(g) and a conductive film that can beused as the wiring ML(h) to be used for the sensing region 401. Theconductive films obtained by dividing a conductive film into a pluralityof regions can each have a comb-like shape, for example (see anelectrode CE(1), an electrode ME(1), and an electrode ME(2) in FIGS. 23Aand 23B). In this manner, the divided conductive films can be used aselectrodes of sensing elements.

For example, a conductive film that can be used as the wiring CL(1), aconductive film that can be used as the wiring ML(1), and a conductivefilm that can be used as the wiring ML(2), which are obtained bydividing a conductive film, are adjacent to each other in an adjoiningportion X0 (see FIGS. 22A and 22C and FIGS. 23A and 23B).

A sensing element 475(g,h) is electrically connected to the wiring CL(g)and the wiring ML(h) (see FIG. 22A).

The wiring CL(g) has a function of supplying a control signal (Tx), andthe wiring ML(h) has a function of receiving a sensing signal (Rx).

The wiring ML(h) includes a conductive film BR(g,h) (see FIG. 22B). Theconductive film BR(g,h) includes a region overlapping with the wiringCL(g).

Note that the sensing element 475(g,h) includes an insulating film. Theinsulating film includes a region positioned between the wiring ML(h)and the conductive film BR(g,h). Thus, a short circuit between thewiring ML(h) and the conductive film BR(g,h) can be prevented.

The electrode CE(1) is electrically connected to the wiring CL(1), andthe electrode ME(1) is electrically connected to the wiring ML(1) (FIGS.23A and 23B).

In a similar manner, an electrode CE(g) is electrically connected to thewiring CL(g), and an electrode ME(h) is electrically connected to thewiring ML(h).

A sensing element 475(1,1) senses a touch by detecting a change in thevalue of the capacitance formed between the electrode CE(1) and theelectrode ME(1) (see FIGS. 23A and 23B).

In a similar manner, the sensing element 475(g,h) senses a touch bydetecting a change in the value of the capacitance formed between theelectrode CE(g) and the electrode ME(h).

Conductive films which can be formed in the same process can be used asthe wiring CL(1) and the electrode CE(1). Conductive films which can beformed in the same process can be used as the wiring ML(1) and theelectrode ME(1) (see FIGS. 23A and 23B).

In a similar manner, conductive films which can be formed in the sameprocess can be used as the wiring CL(g) and the electrode CE(g).Conductive films which can be formed in the same process can be used asthe wiring ML(h) and the electrode ME(h).

For example, a light-transmitting conductive film can be used as each ofthe electrodes CE(g) and ME(h). Alternatively, a conductive film havingan opening or a comb-like shape in a region overlapping with the pixelcan be used as each of the wirings CL(g) and ML(h). Accordingly, anobject that approaches the region overlapping with the display panel canbe sensed without disturbing display on the display panel.

Note that this embodiment can be combined with any of the otherembodiments in this specification as appropriate.

Embodiment 8

In this embodiment, structure examples of the touch panel described inEmbodiment 7 will be described. Note that in this embodiment, aprojected capacitive (mutual capacitive) touch panel will be described.

FIGS. 24A to 24D, FIGS. 25A and 25B, FIGS. 26A and 26B, and FIGS. 27Aand 27B are each a schematic cross-sectional view of a touch sensorincluding the touch panel 400 and a display panel. Note that theschematic cross-sectional views in FIGS. 24A to 24D, FIGS. 25A and 25B,FIGS. 26A and 26B, and FIGS. 27A and 27B illustrate only components thatare necessary for the description of the operation of the touch sensor.For example, an element such as a transistor or a light-transmittingelement may be provided over a substrate 411 but is omitted in thesedrawings.

The touch sensor illustrated in FIG. 24A includes the substrate 411, asubstrate 412, an FPC 413, a conductive film 414, a liquid crystalelement 420, a coloring film 431, a conductive film 441, and the like.

The liquid crystal element 420 includes a conductive film 421, aconductive film 422, and a liquid crystal 423. The conductive film 422is provided over the conductive film 421 with an insulating film 424positioned therebetween. The conductive film 421 functions as a commonelectrode of the liquid crystal element 420, and the conductive film 422functions as a pixel electrode.

The conductive film 421 and the conductive film 422 are arranged suchthat an electric field which intersects the thickness direction (thedirection A1-A2 in the drawing) of the liquid crystal 423 is formed. Asthe liquid crystal 423, a liquid crystal material which operates in anin-plane-switching (IPS) mode, a fringe field switching (FFS) mode, or avertical alignment in-plane-switching (VA-IPS) mode can be used.

The touch sensor can perform sensing by utilizing the capacitance formedbetween the conductive film 441 provided on the substrate 412 side andthe conductive film 421 functioning as one of a pair of electrodes ofthe liquid crystal element 420.

The conductive film 441 is provided over a surface of the substrate 412on the display surface side (the side opposite to the substrate 411). Inaddition, the conductive film 441 is electrically connected to an FPC443 provided on the substrate 412 side. Through the conductive film 414,the conductive film 421 is electrically connected to the FPC 413provided on the substrate 411 side.

In the touch sensor illustrated in FIG. 24A, the conductive film 421 andthe conductive film 422 may serve as a pixel electrode and a commonelectrode, respectively, and a touch may be sensed by utilizing thecapacitance formed between the conductive film 441 and the conductivefilm 422. FIG. 24B is a schematic view illustrating the case.

In the touch sensor illustrated in FIG. 24A, the conductive film 441 maybe provided between the substrate 412 and the liquid crystal 423. FIG.24C is a schematic view illustrating the case.

In the touch sensor illustrated in FIG. 24B, the conductive film 441 maybe provided between the substrate 412 and the liquid crystal 423. FIG.24D is a schematic view illustrating the case.

In the structures illustrated in FIGS. 24A to 24D, one electrode of theliquid crystal element 420 can also serve as one of a pair of electrodesof the touch sensor. Consequently, the process can be simplified and themanufacturing cost can be reduced.

In the touch sensor illustrated in FIG. 24A, the conductive film 441 andthe FPC 443 are not necessarily provided. FIG. 25A is a schematic viewillustrating the case.

In FIG. 25A, conductive films 421 a and 421 b each serving as a commonelectrode of the liquid crystal element 420 also serve as the pair ofelectrodes of the touch sensor.

In the touch sensor illustrated in FIG. 25A, the conductive film 422 maybe used as a common electrode. FIG. 25B is a schematic cross-sectionalview illustrating the case. In FIG. 25B, a conductive film 422 a and aconductive film 422 b serve as the pair of electrodes of the touchsensor.

In the structure illustrated in FIG. 25A or 25B, one electrode of theliquid crystal element 420 can serve as both of the pair of electrodesof the touch sensor. Accordingly, the manufacturing process can besimplified as compared with the cases in FIGS. 24A and 24B.

In the touch sensor illustrated in FIG. 24A, the pair of electrodes ofthe touch sensor may be formed of only the conductive film 441. FIG. 26Ais a schematic cross-sectional view illustrating the case.

In FIG. 26A, a conductive film 441 a and a conductive film 441 b whichare provided over the substrate 412 serve as the pair of electrodes ofthe touch sensor.

In the touch sensor illustrated in FIG. 26A, the conductive film 441 aand the conductive film 441 b may be provided between the substrate 412and the liquid crystal 423. FIG. 26B is a schematic cross-sectional viewillustrating the case.

In FIG. 26A or 26B, the conductive film 441 a and the conductive film441 b are spaced apart from the electrodes of the liquid crystal element420 (the conductive film 421 and the conductive film 422). Therefore, anelectric field formed by the conductive film 441 a and the conductivefilm 441 b does not interfere with an electric field formed by theliquid crystal element 420. Furthermore, the conductive film 441 a andthe conductive film 441 b are spaced apart from a wiring, a transistor,and the like which are formed over the substrate 411 and might serve asnoise generation sources. Therefore, the touch sensor illustrated inFIG. 26A or 26B can have a high touch sensitivity.

In the case where the electrodes of the touch sensor are arranged as inFIG. 26A or 26B, a liquid crystal that enables display by application ofan electric field perpendicular to the substrate 411 can be used as theliquid crystal 423. FIGS. 27A and 27B are schematic cross-sectionalviews illustrating the case.

In FIGS. 27A and 27B, the conductive film 421 and the conductive film422 are vertically stacked with the liquid crystal 423 positionedtherebetween. Also in this case, an electric field formed by theconductive film 441 a and the conductive film 441 b does not interferewith an electric field formed by the liquid crystal element 420. Theliquid crystal 423 can employ a twisted nematic (TN) mode, a verticalalignment (VA) mode, a multi-domain vertical alignment (MVA) mode, anoptically compensated birefringence (OCB) mode, or the like.

Note that this embodiment can be combined with any of the otherembodiments in this specification as appropriate.

Embodiment 9

In this embodiment, examples of an electronic device in which thedisplay device described in the above embodiment can be used will bedescribed.

<Laptop Personal Computer>

FIG. 28A illustrates a laptop personal computer including a housing5401, a display portion 5402, a keyboard 5403, a pointing device 5404,and the like. The display device of one embodiment of the presentinvention can be used for the display portion 5402.

<Smart Watch>

FIG. 28B illustrates a smart watch which is one of wearable terminals.The smart watch includes a housing 5901, a display portion 5902,operation buttons 5903, an operator 5904, a band 5905, and the like. Thedisplay device of one embodiment of the present invention can be usedfor the smart watch. A display device with a position input function maybe used for the display portion 5902. The position input function can beadded by providing a touch panel in the display device. Alternatively,the position input function can be added by providing a photoelectricconversion element called a photosensor in a pixel portion of thedisplay device. As the operation buttons 5903, any of a power switch forstarting the smart watch, a button for operating an application of thesmart watch, a volume control button, a switch for turning on or off thedisplay portion 5902, and the like can be provided. Although the smartwatch illustrated in FIG. 28B includes two operation buttons 5903, thenumber of operation buttons included in the smart watch is not limitedto two. The operator 5904 functions as a crown for time adjustment ofthe smart watch. The operator 5904 may be used as an input interface foroperating an application of the smart watch as well as the crown fortime adjustment. Although the smart watch illustrated in FIG. 28Bincludes the operator 5904, one embodiment of the present invention isnot limited thereto and the operator 5904 is not necessarily provided.

<Video Camera>

FIG. 28C illustrates a video camera including a first housing 5801, asecond housing 5802, a display portion 5803, operation keys 5804, a lens5805, a joint 5806, and the like. The display device of one embodimentof the present invention can be used for the video camera. The operationkeys 5804 and the lens 5805 are provided in the first housing 5801, andthe display portion 5803 is provided in the second housing 5802. Thefirst housing 5801 and the second housing 5802 are connected to eachother with the joint 5806, and the angle between the first housing 5801and the second housing 5802 can be changed with the joint 5806. Imagesdisplayed on the display portion 5803 may be switched in accordance withthe angle at the joint 5806 between the first housing 5801 and thesecond housing 5802.

<Mobile Phone>

FIG. 28D illustrates a mobile phone serving as an information terminal.The mobile phone includes a housing 5501, a display portion 5502, amicrophone 5503, a speaker 5504, and operation buttons 5505. The displaydevice of one embodiment of the present invention can be used for themobile phone. A display device with a position input function may beused for the display portion 5502. The position input function can beadded by providing a touch panel in the display device. Alternatively,the position input function can be added by providing a photoelectricconversion element called a photosensor in a pixel area of the displaydevice. As operation buttons 5505, any of a power switch for startingthe mobile phone, a button for operating an application of the mobilephone, a volume control button, a switch for turning on or off thedisplay portion 5502, and the like can be provided.

Although the mobile phone illustrated in FIG. 28D includes two operationbuttons 5505, the number of operation buttons included in the mobilephone is not limited to two. Although not illustrated, a light-emittingdevice may be included in the mobile phone illustrated in FIG. 28D to beused as a flashlight or a lighting device.

<Television Device>

FIG. 28E is a perspective view illustrating a television device. Thetelevision device includes a housing 9000, a display portion 9001, aspeaker 9003, an operation key 9005 (including a power switch or anoperation switch), a connection terminal 9006, a sensor 9007 (a sensorhaving a function of measuring force, displacement, position, speed,acceleration, angular velocity, rotational frequency, distance, light,liquid, magnetism, temperature, chemical substance, sound, time,hardness, electric field, current, voltage, electric power, radiation,flow rate, humidity, gradient, oscillation, odor, or infrared rays), andthe like. The television device can include the display portion 9001having a large screen size of, for example, 50 inches or more or 100inches or more.

<Moving Vehicle>

The above-described display device can also be used around a driver'sseat in an automobile, which is a moving vehicle.

FIG. 28F illustrates a front glass and its vicinity inside anautomobile, for example. FIG. 28F illustrates a display panel 5701, adisplay panel 5702, and a display panel 5703 which are attached to adashboard, and a display panel 5704 attached to a pillar.

The display panels 5701 to 5703 can display a variety of kinds ofinformation such as navigation information, a speedometer, a tachometer,a mileage, a fuel meter, a gearshift indicator, and air-conditionsetting. The content, layout, and the like of the display on the displaypanels can be changed freely to suit the user's preferences, so that thedesign can be improved. The display panels 5701 to 5703 can also be usedas lighting devices.

The display panel 5704 can compensate for the view obstructed by thepillar (blind areas) by showing an image taken by an imaging unitprovided in the car body. That is, by displaying an image taken by theimaging unit provided on the outside of the automobile, blind areas canbe eliminated and safety can be increased. In addition, showing an imageso as to compensate for the area which the driver cannot see makes itpossible for the driver to confirm safety easily and comfortably. Thedisplay panel 5704 can also be used as a lighting device.

Although not illustrated, a microphone and a speaker may be included ineach of the electronic devices illustrated in FIGS. 28A, 28B, 28E, and28F. The electronic devices with this structure can have an audio inputfunction, for example.

Although not illustrated, a camera may be included in each of theelectronic devices illustrated in FIGS. 28A, 28B, 28D to 28F.

Although not illustrated, a sensor (a sensor having a function ofmeasuring force, displacement, position, speed, acceleration, angularvelocity, rotational frequency, distance, light, liquid, magnetism,temperature, chemical substance, sound, time, hardness, electric field,current, voltage, electric power, radiation, flow rate, humidity,gradient, oscillation, odor, infrared rays, or the like) may be includedinside the housing of each of the electronic devices illustrated inFIGS. 28A to 28F. In particular, when the mobile phone illustrated inFIG. 28D is provided with a sensing device which includes a sensor forsensing inclination, such as a gyroscope sensor or an accelerationsensor, the orientation of the mobile phone (the orientation of themobile phone with respect to the vertical direction) can be determinedto automatically change the display on the screen of the display portion5502 in accordance with the orientation of the mobile phone.

Although not illustrated, a device for obtaining biological informationsuch as information on fingerprints, veins, iris, voice prints, or thelike may be included in each of the electronic devices illustrated inFIGS. 28A to 28F. The electronic devices with this structure can eachhave a biometric identification function.

A flexible base may be used for the display portion of each of theelectronic devices illustrated in FIGS. 28A to 28F. Specifically, thedisplay portion may have a structure in which a transistor, a capacitor,a display element, and the like are provided over a flexible base. Withthis structure, an electronic device with a housing having a curvedsurface can be obtained as well as an electronic device with a housinghaving a flat surface, such as the electronic devices illustrated inFIGS. 28A to 28F.

This embodiment can be combined with any of the other embodiments inthis specification as appropriate.

(Notes on Description of this Specification and the Like)

The following are notes on the description of the structures in theabove embodiments.

<Notes on One Embodiment of the Present Invention Described inEmbodiments>

One embodiment of the present invention can be constituted byappropriately combining the structure described in an embodiment withany of the structures described in the other embodiments. In addition,in the case where a plurality of structure examples is described in oneembodiment, some of the structure examples can be combined asappropriate.

Note that a content (or part thereof) described in one embodiment can beapplied to, combined with, or replaced with another content (or partthereof) described in the embodiment and/or a content (or part thereof)described in another embodiment or other embodiments.

Note that in each embodiment, a content described in the embodiment is acontent described with reference to a variety of diagrams or a contentdescribed with text disclosed in this specification.

Note that by combining a diagram (or part thereof) described in oneembodiment with another part of the diagram, another diagram (or partthereof) described in the embodiment, and/or a diagram (or part thereof)described in another embodiment or other embodiments, much more diagramscan be formed.

<Notes on Ordinal Numbers>

In this specification and the like, ordinal numbers such as “first”,“second”, and “third” are used to avoid confusion among components.Thus, the terms do not limit the number or order of components. In thisspecification and the like, for example, a “first” component in oneembodiment can be referred to as a “second” component in anotherembodiment or a claim. Furthermore, in this specification and the like,for example, a “first” component in one embodiment can be omitted inanother embodiment or a claim.

<Notes on the Description of Drawings>

Embodiments are described with reference to drawings. However, theembodiments can be implemented in various modes. It is readilyappreciated by those skilled in the art that modes and details can bechanged in various ways without departing from the spirit and scope ofthe present invention. Thus, the present invention should not beinterpreted as being limited to the description of the embodiments. Notethat in the structures of the embodiments of the invention, the sameportions or portions having similar functions are denoted by the samereference numerals in different drawings, and the description of suchportions is not repeated.

In this specification and the like, terms for describing arrangement,such as “over” and “under”, are used for convenience to describe thepositional relation between components with reference to drawings. Thepositional relation between components is changed as appropriatedepending on the direction in which each component is described.Therefore, terms for describing arrangement are not limited to thoseused in this specification and can be changed to other terms asappropriate depending on the situation.

The term “over” or “under” does not necessarily mean that a component isplaced directly over or directly under and in direct contact withanother component. For example, the expression “an electrode B over aninsulating layer A” does not necessarily mean that the electrode B isformed over and in direct contact with the insulating layer A and caninclude the case where another component is provided between theinsulating layer A and the electrode B.

In the drawings, the size, the layer thickness, or the region isdetermined arbitrarily for description convenience. Therefore, the scaleis not necessarily limited to that illustrated in the drawings. Notethat the drawings are schematically illustrated for clarity, and shapesor values are not limited to those illustrated in the drawings. Forexample, variation in signal, voltage, or current due to noise ordifference in timing can be included.

In a drawing such as a perspective view, some components might not beillustrated for clarity of the drawing.

In the drawings, the same components, components having similarfunctions, components formed of the same material, or components formedat the same time, or the like are denoted by the same reference numeralsin some cases, and the description thereof is not repeated in somecases.

<Notes on Expressions that can be Rephrased or Reworded>

In this specification and the like, in description of the connectionrelation of a transistor, the terms “one of a source and a drain” (or afirst electrode or a first terminal) and “the other of the source andthe drain” (or a second electrode or a second terminal) are used. Thisis because a source and a drain of a transistor are interchangeabledepending on the structure, operation conditions, or the like of thetransistor. Note that the source or the drain of the transistor can alsobe referred to as a source (or drain) terminal, a source (or drain)electrode, or the like as appropriate depending on the situation. Inthis specification and the like, two terminals except a gate may bereferred to as a first terminal and a second terminal or as a thirdterminal and a fourth terminal. In this specification and the like, inthe case where a transistor has two or more gates (such a structure isreferred to as a dual-gate structure in some cases), these gates may bereferred to as a first gate and a second gate or a front gate and a backgate. In particular, the term “front gate” can be replaced with a simpleterm “gate”. The term “back gate” can be replaced with a simple term“gate”. Note that a “bottom gate” refers to a terminal which is formedbefore a channel formation region in manufacture of a transistor, and a“top gate” refers to a terminal which is formed after a channelformation region in manufacture of a transistor.

A transistor includes three terminals called a gate, a source, and adrain. A gate is a terminal that controls the conduction state of atransistor. Depending on the channel type of the transistor or thelevels of potentials supplied to the terminals, one of terminals (aninput terminal or an output terminal) functions as a source and theother functions as a drain. Therefore, the terms “source” and “drain”are interchangeable in this specification and the like. In thisspecification and the like, the two terminals except the gate may bereferred to as a first terminal and a second terminal or as a thirdterminal and a fourth terminal.

In this specification and the like, the term “electrode” or “wiring”does not limit the function of a component. For example, an “electrode”is used as part of a “wiring” in some cases, and vice versa.Furthermore, the term “electrode” or “wiring” can also mean acombination of a plurality of “electrodes” or “wirings” formed in anintegrated manner.

In this specification and the like, “voltage” and “potential” can bereplaced with each other. The term “voltage” refers to a potentialdifference from a reference potential. When the reference potential is aground potential, for example, “voltage” can be replaced with“potential”. The ground potential does not necessarily mean 0 V. Notethat a potential is a relative value, and a potential supplied towirings or the like may be changed depending on the reference potential.

In this specification and the like, the terms “film”, “layer”, and thelike can be replaced with each other depending on the circumstances orsituation. For example, the term “conductive layer” can be changed intothe term “conductive film” in some cases. Moreover, the term “insulatingfilm” can be changed into the term “insulating layer” in some cases.Alternatively, another term can be used instead of a term including“film” or “layer” depending on the circumstances or situation. Forexample, the term “conductive layer” or “conductive film” can be changedinto the term “conductor” in some cases. For example, the term“insulating layer” or “insulating film” can be changed into the term“insulator” in some cases.

In this specification and the like, the terms “wiring”, “signal line”,“power supply line”, and the like can be replaced with each otherdepending on the circumstances or situation. For example, the term“wiring” can be changed into the term “signal line” or “power supplyline” in some cases. The term “signal line”, “power supply line”, or thelike can be changed into the term “wiring” in some cases. The term“power supply line” or the like can be changed into the term “signalline” or the like in some cases, and vice versa. The term “potential”that is supplied to a wiring can be changed into the term “signal” orthe like depending on the circumstances or situation, and vice versa.

<Notes on Definitions of Terms>

The following are definitions of the terms mentioned in the aboveembodiments.

«Impurity in Semiconductor»

Impurities in a semiconductor refer to, for example, elements other thanthe main components of a semiconductor layer. For example, an elementwith a concentration of lower than 0.1 atomic % is an impurity. When animpurity is contained, the density of states (DOS) may be formed in asemiconductor, the carrier mobility may be decreased, or thecrystallinity may be decreased, for example. In the case where thesemiconductor is an oxide semiconductor, examples of an impurity whichchanges the characteristics of the semiconductor include the Group 1elements, the Group 2 elements, the Group 13 elements, the Group 14elements, the Group 15 elements, and transition metals other than themain components of the semiconductor, specifically, hydrogen (includingthat contained in water), lithium, sodium, silicon, boron, phosphorus,carbon, nitrogen, and the like. In the case of an oxide semiconductor,an oxygen vacancy may be formed by entry of an impurity such ashydrogen. In the case where the semiconductor is a silicon layer,examples of an impurity which changes the characteristics of thesemiconductor include oxygen, the Group 1 elements except hydrogen, theGroup 2 elements, the Group 13 elements, and the Group 15 elements.

«Transistor»

In this specification, a transistor is an element having at least threeterminals: a gate, a drain, and a source. The transistor has a channelformation region between the drain (a drain terminal, a drain region, ora drain electrode) and the source (a source terminal, a source region,or a source electrode). When a potential difference is applied betweenthe gate and the source, a current can flow through the channelformation region.

Furthermore, functions of a source and a drain may be switched whentransistors having different polarities are employed or the direction ofcurrent flow is changed in circuit operation, for example. Therefore,the terms “source” and “drain” can be replaced with each other in thisspecification and the like.

«Switch»

In this specification and the like, a switch is conducting or notconducting (is turned on or off) to determine whether current flowstherethrough or not. Alternatively, a switch is an element having afunction of selecting and changing a current path.

For example, an electrical switch or a mechanical switch can be used.That is, the switch is not limited to a certain element as long as itcan control a current.

A transistor (e.g., a bipolar transistor or a MOS transistor), a diode(e.g., a PN diode, a PIN diode, a Schottky diode, ametal-insulator-metal (MIM) diode, a metal-insulator-semiconductor (MIS)diode, or a diode-connected transistor), a logic circuit in which suchelements are combined, or the like can be used as an electrical switch.

When a transistor is used as a switch, an “on state” of the transistorrefers to a state in which a source electrode and a drain electrode ofthe transistor are electrically short-circuited. Furthermore, an “offstate” of the transistor refers to a state in which the source electrodeand the drain electrode of the transistor are electrically disconnected.If the transistor operates just as a switch, there is no particularlimitation on the polarity (conductivity type) of the transistor.

An example of a mechanical switch is a switch formed using amicroelectromechanical systems (MEMS) technology, such as a digitalmicromirror device (DMD). Such a switch includes an electrode which canbe moved mechanically, and its conduction and non-conduction iscontrolled by the movement of the electrode.

«Connection»

In this specification and the like, the expression “X and Y areconnected” can mean that X and Y are electrically connected, that X andY are functionally connected, and that X and Y are directly connected.Accordingly, without being limited to a predetermined connectionrelation, for example, a connection relation other than that shown in adrawing or text is also possible.

Here, X, Y, and the like each denote an object (e.g., a device, anelement, a circuit, a wiring, an electrode, a terminal, a conductivefilm, or a layer).

For example, in the case where X and Y are electrically connected, oneor more elements that enable electrical connection between X and Y(e.g., a switch, a transistor, a capacitor, an inductor, a resistor, adiode, a display element, a light-emitting element, and/or a load) canbe connected between X and Y. A switch is controlled to be on or off.That is, a switch is conducting or not conducting (is turned on or off)to determine whether a current flows therethrough or not.

For example, in the case where X and Y are functionally connected, oneor more circuits that enable functional connection between X and Y(e.g., a logic circuit such as an inverter, a NAND circuit, or a NORcircuit; a signal converter circuit such as a DA converter circuit, anAD converter circuit, or a gamma correction circuit; a potential levelconverter circuit such as a power supply circuit (e.g., a step-upcircuit and a step-down circuit) or a level shifter circuit for changingthe potential level of a signal; a voltage source; a current source; aswitching circuit; an amplifier circuit such as a circuit that canincrease the signal amplitude, the amount of current, or the like, anoperational amplifier, a differential amplifier circuit, a sourcefollower circuit, or a buffer circuit; a signal generation circuit; amemory circuit; and/or a control circuit) can be connected between X andY. For example, even when another circuit is interposed between X and Y,X and Y are functionally connected if a signal output from X istransmitted to Y.

Note that the explicit expression “X and Y are electrically connected”can mean that X and Y are electrically connected (i.e., X and Y areconnected with another element or another circuit positionedtherebetween), that X and Y are functionally connected (i.e., X and Yare functionally connected with another circuit positionedtherebetween), and that X and Y are directly connected (i.e., X and Yare connected without another element or another circuit positionedtherebetween). That is, the explicit expression “X and Y areelectrically connected” is the same as the explicit simple expression “Xand Y are connected”.

For example, any of the following expressions can be used for the casewhere a source (or a first terminal or the like) of a transistor iselectrically connected to X through (or not through) Z1 and a drain (ora second terminal or the like) of the transistor is electricallyconnected to Y through (or not through) Z2, or the case where a source(or a first terminal or the like) of a transistor is directly connectedto one part of Z1 and another part of Z1 is directly connected to Xwhile a drain (or a second terminal or the like) of the transistor isdirectly connected to one part of Z2 and another part of Z2 is directlyconnected to Y.

Examples of the expressions include, “X, Y, a source (or a firstterminal or the like) of a transistor, and a drain (or a second terminalor the like) of the transistor are electrically connected to each other,and X, the source (or the first terminal or the like) of the transistor,the drain (or the second terminal or the like) of the transistor, and Yare electrically connected to each other in this order”, “a source (or afirst terminal or the like) of a transistor is electrically connected toX, a drain (or a second terminal or the like) of the transistor iselectrically connected to Y, and X, the source (or the first terminal orthe like) of the transistor, the drain (or the second terminal or thelike) of the transistor, and Y are electrically connected to each otherin this order”, and “X is electrically connected to Y through a source(or a first terminal or the like) and a drain (or a second terminal orthe like) of a transistor, and X, the source (or the first terminal orthe like) of the transistor, the drain (or the second terminal or thelike) of the transistor, and Y are provided to be connected in thisorder”. When the connection order in a circuit configuration is definedby an expression similar to the above examples, a source (or a firstterminal or the like) and a drain (or a second terminal or the like) ofa transistor can be distinguished from each other to specify thetechnical scope. Note that one embodiment of the present invention isnot limited to these expressions that are just examples. Here, X, Y, Z1,and Z2 each denote an object (e.g., a device, an element, a circuit, awiring, an electrode, a terminal, a conductive film, and a layer).

Even when independent components are electrically connected to eachother in a circuit diagram, one component has functions of a pluralityof components in some cases. For example, when part of a wiring alsofunctions as an electrode, one conductive film functions as the wiringand the electrode. Thus, “electrical connection” in this specificationincludes in its category such a case where one conductive film hasfunctions of a plurality of components.

«Parallel and Perpendicular»

In this specification, the term “parallel” indicates that the angleformed between two straight lines is greater than or equal to −10° andless than or equal to 10°, and accordingly also includes the case wherethe angle is greater than or equal to −5° and less than or equal to 5°.In addition, the term “substantially parallel” indicates that the angleformed between two straight lines is greater than or equal to −30° andless than or equal to 30°. In addition, the term “perpendicular”indicates that the angle formed between two straight lines is greaterthan or equal to 80° and less than or equal to 100°, and accordinglyalso includes the case where the angle is greater than or equal to 85°and less than or equal to 95°. In addition, the term “substantiallyperpendicular” indicates that the angle formed between two straightlines is greater than or equal to 60° and less than or equal to 120°.

This application is based on Japanese Patent Application Serial No.2016-206479 filed with Japan Patent Office on Oct. 21, 2016, the entirecontents of which are hereby incorporated by reference.

What is claimed is:
 1. A method for operating an electronic devicecomprising a display device and a touch sensor, the method comprising afirst step, a second step, a third step, and a fourth step, wherein thefirst step comprises: a first judgment step of judging whether the touchsensor senses a touch in a first period in a normal driving state of thedisplay device; proceeding to the second step in the case where thefirst judgment step confirms that no touch is sensed; and proceeding tothe third step in the case where the first judgment step confirms that atouch is sensed, wherein the second step comprises: bringing the touchsensor into a resting state or reducing a drive frequency of the touchsensor, wherein the third step comprises: a second judgment step ofjudging whether the display device is brought into a resting state or adrive frequency of the display device is reduced; and proceeding to thefourth step in the case where the second judgment step confirms that thedisplay device is brought into the resting state or the drive frequencyof the display device is reduced, and wherein the fourth step comprises:a third judgment step of judging whether touches are constantly sensedin a state whether the display device is brought into a resting state ora drive frequency of the display device is reduced; and proceeding tothe second step in the case where the third judgment step confirms thattouches are constantly sensed.
 2. The method for operating an electronicdevice according to claim 1, wherein the display device comprises areflective liquid crystal element and one of a light-emitting elementand a transmissive liquid crystal element.
 3. The method for operatingan electronic device according to claim 1, wherein the display devicecomprises a reflective liquid crystal element, and wherein thereflective liquid crystal element and the touch sensor share oneelectrode.
 4. The method for operating an electronic device according toclaim 1, wherein the display device comprises a transistor comprising anoxide semiconductor in a channel formation region.